Ultimate Calming Solution Toner
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Pyunkang Yul Ultimate Calming Solution TonerIngredients explained
Good old water, aka H2O. The most common skincare ingredient of all. You can usually find it right in the very first spot of the ingredient list, meaning it’s the biggest thing out of all the stuff that makes up the product.
It’s mainly a solvent for ingredients that do not like to dissolve in oils but rather in water.
Once inside the skin, it hydrates, but not from the outside - putting pure water on the skin (hello long baths!) is drying.
One more thing: the water used in cosmetics is purified and deionized (it means that almost all of the mineral ions inside it is removed). Like this, the products can stay more stable over time.
- A natural moisturizer that’s also in our skin
- A super common, safe, effective and cheap molecule used for more than 50 years
- Not only a simple moisturizer but knows much more: keeps the skin lipids between our skin cells in a healthy (liquid crystal) state, protects against irritation, helps to restore barrier
- Effective from as low as 3% with even more benefits for dry skin at higher concentrations up to 20-40%
- High-glycerin moisturizers are awesome for treating severely dry skin
Butylene glycol, or let’s just call it BG, is a multi-tasking colorless, syrupy liquid. It’s a great pick for creating a nice feeling product.
BG’s main job is usually to be a solvent for the other ingredients. Other tasks include helping the product to absorb faster and deeper into the skin (penetration enhancer), making the product spread nicely over the skin (slip agent), and attracting water (humectant) into the skin.
It’s an ingredient whose safety hasn’t been questioned so far by anyone (at least not that we know about). BG is approved by Ecocert and is also used enthusiastically in natural products. BTW, it’s also a food additive.
A clear, colorless liquid that works as a solvent and viscosity decreasing ingredient. It also has great skin-moisturizing abilities.
A traditional East Asian medicine that has a couple of recent studies to back up its positive effects on the skin.
It seems to have potent anti-inflammatory activity, it's a mild antioxidant and also has strong anti-bacterial effect for acne causing bacteria, Propionibacterium acne.
We don't have description for this ingredient yet.
A traditional Chinese herbal medicine loaded with potent antioxidant and anti-inflammatory flavonoids such as baicalin, baicalein, and wogonin.
If that would not be enough, Skullcap Root is also claimed to have antimicrobial and antifungal properties (also against P.acnes and Malassezia furfur) as well as some skin-brightening activity. A multi-functional skin-goodie.
A sugar beet-derived amino acid derivative with nice skin protection and moisturization properties. Betaine's special thing is being an osmolyte, a molecule that helps to control cell-water balance. It is also a natural osmoprotectant, meaning that it attracts water away from the protein surface and thus protects them from denaturation and increases their thermodynamic stability.
It also gives sensorial benefits to the formula and when used in cleansers, it helps to make them milder and gentler.
We don't have description for this ingredient yet.
A handy multifunctional ingredient that works as a preservative booster, as well as an antioxidant and soothing agent.
Though its long name does not reveal it, this polymer molecule (big molecule from repeated subunits or monomers) is a relative to the super common, water-loving thickener, Carbomer. Both of them are big molecules that contain acrylic acid units, but Acrylates/C10-30 Alkyl Acrylate Crosspolymer also contains some other monomers that are hydrophobic, i.e. water-hating.
This means that our molecule is part water- and part oil-loving, so it not only works as a thickener but also as an emulsion stabilizer. It is very common in gel-type formulas that also contain an oil-phase as well as in cleansers as it also works with most cleansing agents (unlike a lot of other thickeners).
A semi-essential (infants cannot synthesize it, but adults can) amino acid that is one of the primary building blocks of hair keratin and skin collagen. It's a natural moisturizing factor, a skin hydrator and might also help to speed up wound healing.
Arginine usually has a positive charge (cationic) that makes it substantive to skin and hair (those are more negatively charged surfaces) and an excellent film former. Thanks to the positive charge, it also creates a complex with AHAs (AHAs like to lose a hydrogen ion and be negatively charged, so the positive and the negative ions attract each other) that causes a "time-release AHA effect" and reduces the irritation associated with AHAs.
A really multi-functional helper ingredient that can do several things in a skincare product: it can bring a soft and pleasant feel to the formula, it can act as a humectant and emollient, it can be a solvent for some other ingredients (for example it can help to stabilize perfumes in watery products) and it can also help to disperse pigments more evenly in makeup products. And that is still not all: it can also boost the antimicrobial activity of preservatives.
We don't have description for this ingredient yet.
If you have spotted ethylhexylglycerin on the ingredient list, most probably you will see there also the current IT-preservative, phenoxyethanol. They are good friends because ethylhexylglycerin can boost the effectiveness of phenoxyethanol (and other preservatives) and as an added bonus it feels nice on the skin too.
Also, it's an effective deodorant and a medium spreading emollient.
Citric acid comes from citrus fruits and is an AHA. If these magic three letters don’t tell you anything, click here and read our detailed description on glycolic acid, the most famous AHA.
So citric acid is an exfoliant, that can - just like other AHAs - gently lift off the dead skin cells of your skin and make it more smooth and fresh.
There is also some research showing that citric acid with regular use (think three months and 20% concentration) can help sun-damaged skin, increase skin thickness and some nice hydrating things called glycosaminoglycans in the skin.
But according to a comparative study done in 1995, citric acid has less skin improving magic properties than glycolic or lactic acid. Probably that’s why citric acid is usually not used as an exfoliant but more as a helper ingredient in small amounts to adjust the pH of a formulation.
- It’s a polyhydroxy acid (PHA), that is often referred to as next generation AHA
- It gently lifts off dead skin cells form the skin surface making skin smooth and even
- In the long term it provides anti-aging benefits, like increased skin thickness and decreased wrinkles (though a tad less than even more proven superstar AHAs)
- It’s a great moisturizer and even helps to repair impaired skin barrier
- It’s antioxidant, and does not make your skin more sensitive to the sun
- It can be used even if your skin is very sensitive, rosacea prone or if you are post cosmetic procedure
A castor oil derived, white, lard-like helper ingredient that is used as a solubilizer to put fragrances (those are oil loving things) into water-based products such as toners.
The essential oil coming from steam distillation of freshly harvested, flowering peppermint sprigs. Its major component is menthol that gives the oil its well-known refreshing and cooling properties. Peppermint oil is traditionally used as an inhalant for cold and coughs and there is also some clinical data validating its use against headaches by rubbing a peppermint oil cream on the forehead.
As for skincare, other than the nice grassy-minty smell and the refreshing sensations, we cannot write good things. It can be a skin irritant, so much so that it is a well-known counterirritant for muscle pains creating mild surface irritation to make things better in the deeper layers. But for everyday skincare, counterirritation is not something you wanna do, so we think that peppermint oil is better to avoid, especially if your skin is sensitive.
The essential oil coming from the rind of the orange (the sweet one). In general, the main component of citrus peel oils is limonene (83-97% for sweet orange peel), a super common fragrant ingredient that makes everything smell nice (but counts as a frequent skin sensitizer).
Other than that, citrus peel also contains the problematic compound called furanocoumarin that makes them mildly phototoxic. Orange peel contains less of it than some other citruses (like bergamot or lime), but still, be careful with it especially if it is in a product for daytime use.
The essential oil coming from the fruit (probably the rind) of the bergamot orange. It's a common top note in perfumes and contains (among others) fragrant compounds limonene (37%), linalyl acetate (30%) and linalool (8.8%).
A well-known issue with bergamot oil (apart from the fragrance allergens) is that it contains phototoxic compounds called furanocoumarins, but more and more commonly furanocoumarin-free versions are used in cosmetic products. Still, if you have sensitive skin and prefer fragrance-free products, bergamot oil is not for you.
The fragrant essential oil coming from the whole plant of Rose Geranium. It has a lovely scent with a mix of rose and citrus.
Like most essential oils, it contains antioxidant and antimicrobial components, but the main ones are fragrant constituents (like geraniol and citronellol). Be careful with it, if your skin is sensitive.
It seems to us that squalane is in fashion and there is a reason for it. Chemically speaking, it is a saturated (no double bonds) hydrocarbon (a molecule consisting only of carbon and hydrogen), meaning that it's a nice and stable oily liquid with a long shelf life.
It occurs naturally in certain fish and plant oils (e.g. olive), and in the sebum (the oily stuff our skin produces) of the human skin. As f.c. puts it in his awesome blog post, squalane's main things are "emolliency, surface occlusion, and TEWL prevention all with extreme cosmetic elegance". In other words, it's a superb moisturizer that makes your skin nice and smooth, without being heavy or greasy.
Another advantage of squalane is that it is pretty much compatible with all skin types and skin conditions. It is excellent for acne-prone skin and safe to use even if you have fungi-related skin issues, like seborrhea or fungal acne.
The unsaturated (with double bonds) and hence less stable version of Squalane is Squalene, you can read about it here >>
Unless you live under a rock you must have heard about shea butter. It's probably the most hyped up natural butter in skincare today. It comes from the seeds of African Shea or Karite Trees and used as a magic moisturizer and emollient.
But it's not only a simple emollient, it regenerates and soothes the skin, protects it from external factors (such as UV rays or wind) and is also rich in antioxidants (among others vitamin A, E, F, quercetin and epigallocatechin gallate). If you are looking for rich emollient benefits + more, shea is hard to beat.
Lonicera Japonica, or Japanese Honeysuckle as normal people call it, is a white-flowered honeysuckle known for being a traditional Chinese medicine. Modern research confirms that the plant has a super complex chemical composition with more than 140 compounds identified with possible anti-inflammatory, antibacterial, antiviral, antioxidative and hepatoprotective activities.
As for Lonicera Japonica Flower Extract in skin care, it can have two main roles. The first one is being an anti-inflammatory and soothing ingredient, probably due to chlorogenic acid, a polyphenol thought to be the main bioactive component of the flower.
The other possible role is being a natural preservative. If this is the case, it is coupled with its Italian Honeysuckle cousin to form a broad spectrum antimicrobial preservative blend. You can read about this more here.
A super common emollient that makes your skin feel nice and smooth. It comes from coconut oil and glycerin, it’s light-textured, clear, odorless and non-greasy. It’s a nice ingredient that just feels good on the skin, is super well tolerated by every skin type and easy to formulate with. No wonder it’s popular.
One of the many types of ceramides that can be found naturally in the upper layer of the skin. Ceramides make up about 50% of the goopy stuff that's between our skin cells and play a super important role in having a healthy skin barrier and keeping the skin hydrated. It works even better when combined with its pal, Ceramide 1.
We wrote way more about ceramides at ceramide 1, so click here to know more.
Baobab is a really big, iconic tree native to Africa (here is a nice image of it). It's the largest succulent plant in the world and almost all parts of it have traditional medicinal uses in Africa.
The seed oil, similar to other plant oils, is loaded with things that are good-for-the-skin: it contains skin regenerating vitamin A, antioxidant vitamin E, and vitamin D3 that helps with calcium absorption. It's rich in nourishing fatty acids oleic (30-40%), linoleic (24-34%) and palmitic (18-30%).
Its moisturizing benefits are impressive, it absorbed into the skin quickly and might even improve skin elasticity. A great oil for drier skin types and excellent for eczema and psoriasis.
It's the chemically chopped up version of normal lecithin. Most often it's used to create liposomes and to coat and stabilize other ingredients.
A multi-functional, silky feeling helper ingredient that can do quite many things. It's used as an emulsion stabilizer, solvent and a broad spectrum antimicrobial. According to manufacturer info, it's also a moisturizer and helps to make the product feel great on the skin. It works synergistically with preservatives and helps to improve water-resistance of sunscreens.
When it comes to Tea Tree, the essential oil is the one that steals the show with its well-documented antimicrobial and anti-acne effects. The extract is not very well defined, and it probably contains the active components of the oil in much-reduced concentrations. Manufacturers still mention soothing, antimicrobial, purifying and antiseptic properties for the tea tree extract.
It’s the - sodium form - cousin of the famous NMF, hyaluronic acid (HA). If HA does not tell you anything we have a super detailed, geeky explanation about it here. The TL; DR version of HA is that it's a huge polymer (big molecule from repeated subunits) found in the skin that acts as a sponge helping the skin to hold onto water, being plump and elastic. HA is famous for its crazy water holding capacity as it can bind up to 1000 times its own weight in water.
As far as skincare goes, sodium hyaluronate and hyaluronic acid are pretty much the same and the two names are used interchangeably. As cosmetic chemist kindofstephen writes on reddit "sodium hyaluronate disassociates into hyaluronic acid molecule and a sodium atom in solution".
In spite of this, if you search for "hyaluronic acid vs sodium hyaluronate" you will find on multiple places that sodium hyaluronate is smaller and can penetrate the skin better. Chemically, this is definitely not true, as the two forms are almost the same, both are polymers and the subunits can be repeated in both forms as much as you like. (We also checked Prospector for sodium hyaluronate versions actually used in cosmetic products and found that the most common molecular weight was 1.5-1.8 million Da that absolutely counts as high molecular weight).
What seems to be a true difference, though, is that the salt form is more stable, easier to formulate and cheaper so it pops up more often on the ingredient lists.
If you wanna become a real HA-and-the-skin expert you can read way more about the topic at hyaluronic acid (including penetration-questions, differences between high and low molecular weight versions and a bunch of references to scientific literature).
- Primary fat-soluble antioxidant in our skin
- Significant photoprotection against UVB rays
- Vit C + Vit E work in synergy and provide great photoprotection
- Has emollient properties
- Easy to formulate, stable and relatively inexpensive
It’s a handy multi-tasking ingredient that gives the skin a nice, soft feel. At the same time, it also boosts the effectiveness of other preservatives, such as the nowadays super commonly used phenoxyethanol.
The blend of these two (caprylyl glycol + phenoxyethanol) is called Optiphen, which not only helps to keep your cosmetics free from nasty things for a long time but also gives a good feel to the finished product. It's a popular duo.
It's a special "cross-linked" from of IT-moisturizer, hyaluronic acid (HA). Cross-linked means that "normal" HA pieces (1-2 million Da molecular weight) are chemically bound togeather to create a big, "infinite" mesh.
The special HA mesh has a remarkable water-binding capacity, 5 times more than the already crazy water-binding capacity of "normal" HA. This water filled crosslinked HA gel forms a smooth film on the skin and continuously delivers the bound water, so it gives long-term moisturizing benefits.
Btw, crosslinking HA was developed for dermal fillers (as crosslinking helps their longevity), and this guy is the topical version of FDA approved dermal filler called Hylan B gel. Smearing crosslinked version all over ourselves is a newish thing, and incoming evidence so far suggests that it's a great idea, even better than normal HA.
A very recent, 2016 research article compared the topical moisturizing effect of crosslinked HA (not Hylan B gel specifically, but something called Resilient HA or RHA), HMW-HA and LMW-HA and found that "TEWL (that is trans-epidermal water loss, the water that evaporates from the skin) was reduced by 27.8% with RHA, and by 15.6% with HMW HA, but increased by 55.5% with LMW HA." (You can read much more about HMW and LMW HA here in the geeky details section.)
All in all, we think Sodium Hyaluronate Crosspolymer is an awesome version of HA, probably superior to traditional versions, so be happy to spot it on the ingredient list.
We don't have description for this ingredient yet.
We don't have description for this ingredient yet.
Hydrolyzed Hyaluronic Acid is a low molecular weight, chemically chopped up version of the naturally big molecule and current IT-moisturizer, Hyaluronic Acid (HA). The TL; DR version of HA is that it's a huge polymer (big molecule from repeated subunits) found in the skin that acts as a sponge helping the skin to retain water, making it plump and elastic. As HA is a polymer, the subunits can be repeated many times (as a high-molecular-weight version), or just a few times (as a low-molecular-weight version).
We wrote in detail at HA about how different molecular weight versions do different things both as a component of the skin and as a skincare ingredient, so click here and read about all the details. Hydrolyzed Hyaluronic Acid can also come in different molecular-weight versions with different properties:
- 100-300 kDa version: apart from moisturizing, this size might also help the skin to repair itself by increasing its self-defense. It is also claimed to boost the wound healing process and is especially helpful for sensitive skin types (acne, rosacea, inflammation-related skin diseases).
- 50k Da version: this is the size that is claimed to be able to absorb into the skin and plump up wrinkles, so it is used mainly as an "anti-aging ingredient"
- below 50k, around 10k Da version: there is a Japanese version trade named Hyalo-Oligo that has only a 10k molecular weight and is claimed to penetrate the skin very well, have a unique touch and give deep and long-lasting moisturization. Based on the Evonik-research and the natural role of LMW-HA in the body working as a pro-inflammatory signal molecule, this ultra-low molecular weight version is a controversial ingredient.
If you wanna become a real HA-and-the-skin expert, you can read much more about the topic at hyaluronic acid (including penetration-questions, differences between high and low molecular weight versions and a bunch of references to scientific literature).
Centella Asiatica - or sometimes also called Gotu Kola or Cica - has been used in folk medicine for hundreds of years. It’s traditionally used to improve small wounds, burns and scratches and it’s also a well known anti-inflammatory agent for eczema.
Recently science has taken an interest in Gotu Kola as well and it turns out it really has many active compounds with several benefits. Just for hard-core geeks, the main biologically active compounds are pentacyclic triterpenoid saponins called asiaticoside, madecassoside, asiatic and madecassic acid (also called centellosides).
One of the biological activities of the centellosides is to be able to stimulate GAGs (glycosaminoglycans - polysaccharides that are part of the liquidy stuff between our skin cells), and especially hyaluronic acid synthesis in our skin. This is probably one of the reasons why Centella Asiatica Extract has nice skin moisturizing properties that was confirmed by a 25 people, four weeks study along with Centella's anti-inflammatory effects.
Madecassoside can also help in burn wound healing through increasing antioxidant activity and enhancing collagen synthesis. Asiaticoside was shown to increase antioxidant levels on rats skin when applied at 0.2%.
Centella Asiatica also often shows up in products that try to treat cellulite or striae. Of course, it cannot make a miracle but it might have some effect via regulating microcirculation and normalizing the metabolism in the cells of connective tissues.
Bottom line: Gotu Kola is a great plant ingredient with proven wound healing, anti-inflammatory, and antioxidant properties. Nice to spot on any ingredient list.
Ceramides get quite a lot of hype recently and good news: there is a reason for that. But before we go into the details, let's just quickly define what the heck ceramides are:
They are waxy lipids that can be found naturally in the outer layer of the skin (called stratum corneum - SC). And they are there in big amounts! The goopy stuff between our skin cells is called extracellular matrix that consists mainly of lipids. And ceramides are about 50% of those lipids (the other important ones are cholesterol with 25% and fatty acids with 15%).
Ok, so now we know what ceramides are, let's see what they do in our skin: research shows clearly that they play a super important role in keeping the skin barrier healthy and the skin hydrated. If ceramides in the skin are decreased, more water can evaporate from the skin and there is less water remaining in the skin. So ceramides form kind of a "water-proof" protecting layer and make sure that our skin remains nice and hydrated.
Now the question is only this: If we put ceramides all over our face do they work as well as ceramides already naturally in our skin? Well, the answer is probably a no, but they do work to some extent. The BeautyBrains blog made a fantastic article about ceramides and they have listed a couple of examples about studies showing that ceramides - especially when used in certain ratios with cholesterol and fatty acids - do hydrate the skin and can help to repair the skin barrier.
So far we were writing about ceramides in plural. It's because there are lots of different ceramides, a 2014 article writes that currently 12 base classes of ceramides are known with over 340 specific species. Chemically speaking, ceramides are the connection of a fatty acid and a sphingoid base and both parts can have different variations that result in the different types of ceramides.
Our current one, Ceramide 1, or more recently called Ceramide EOP, was the first one that was identified in 1982 and it's a special snowflake. It contains the essential fatty acid, linoleic acid and has a unique structure. It's believed that ceramide 1 plays a "binding role" in the lipid layers of the extracellular matrix. Along with ceramides 4 and 7, they also play a vital role in epidermal integrity and serve as the main storage areas for linoleic acid (a fatty acid that's also very important for barrier repair).
Oh, and one more thing: alkaline pH inhibits enzymes that help ceramide synthesis in our skin. So if you use a soap and you notice your skin is becoming dry, now you know why.
A type of ceramide that can be found naturally in the upper layer of the skin. Ceramides make up 50% of the goopy stuff that's between our skin cells and play a super important role in having a healthy skin barrier and keeping the skin hydrated.
We have written way more about ceramides at ceramide 1, so click here to know more.
- It’s naturally in our skin and behaves there like a sponge
- It can bind up to 1000 times its own weight in water
- It is a big molecule from repeated subunits (polymer) so different molecular weight versions exist (unfortunately there is no way to determine MW from INCI list only)
- High-molecular-weight-HA (>500 kDa) is an excellent surface hydrator, skin protectant and can act as an osmotic pump helping water-soluble actives to penetrate deeper into the skin
- Low-molecular-weight-HA (< 500 kDa) can hydrate the skin somewhat deeper though it is still a big molecule and works mainly in the epidermis (outer layer of the skin)
- Low-molecular-weight-HA might also help the skin to repair itself by increasing its self-defense (~ 200kDa used in the study)
- Ultra-low-molecular-weight-HA (<50kDa) is a controversial ingredient and might work as a pro-inflammatory signal molecule
It's a super small, chemically chopped up version of sodium hyaluronate. Its trade name is miniHA, and its molecular weight is 10 kDa. This counts as really tiny given that "normal" HA has a molecular weight of 0.5-2 million Da.
To be honest, low molecular weight (LMW), and especially this ultra-low molecular weight HA is a controversial ingredient. On the upside, it can penetrate the skin better (though 10kDa still counts as big!) and might be able to moisturize the deeper layers of the skin where normal HA cannot get. Also, according to the manufacturer of miniHA, it has better antioxidant activity than a 1.6MDa version HA and it also has better sun protection and after-sun repair abilities than the higher MW versions. It also works in synergy with higher molecular weight versions, and the combination of 0.1% 1.45MDa-HA + 0.1% 380 kDa-HA + 0.1% miniHA hydrated the skin significantly better than 0.3% 1.45MDa-HA alone.
On the downside, the biological role of LMW-HA in the skin is being a pro-inflammatory signaling agent and there is a study by another manufacturer called Evonik showing that HA versions with smaller than 50kDa molecular weight might be pro-inflammatory when put on the skin. Granted, the study was only done on reconstituted human epidermis, so it might or might not be like this on real human skin.
If you wanna get confused and read much more about hyaluronic acid and what the different molecular weight versions might or might not do, click here and read our excruciatingly long description.
One of the main biologically active components of the famous medicinal plant, Centella Asiatica, aka Gotu Kola. It has well established wound healing, skin-soothing and antioxidant activities.
There is also a study by La Roche Posay (belongs to L'Oreal) that examined the anti-aging effects of 5% Vitamin C combined with 0.1% Madecassoside. They mention that " Madecassoside is known to induce collagen expression and ⁄ or to modulate inflammatory mediators thus might prevent and correct some signs of aging." The surprisingly long, 6-month study observed "significant improvement of the clinical score for deep and superficial wrinkles, suppleness, firmness, roughness, and skin hydration", but Vitamin C in itself is already an anti-aging superstar, so it is hard to know how much Madecassoside did.
Another promising property of Madecassoside is that it seems to inhibit UV-induced melanin synthesis (test formula with 0.05% MA, used twice a day on 23 volunteers for 8 weeks), making it a great active for hyperpigmentation-prone skin.
If that would not be enough, the French manufacturer (Seppic) also has encouraging in-vivo studies on the molecule. Used at 0.2%, Madecassoside reduces redness and peeling in skin with light atopic dermatitis as well as itching in psoriasis-prone skin.
One of the biologically active components of Gotu Kola that is thought to contribute to the plant extract's well-documented skin regenerating, wound healing, and moisturizing properties.
If you are into Gotu Kola we have some more info at Centella Asiatica Extract and its other biologically active components Madecassoside, Asiaticoside and Asiatic Acid.
One of the main biologically active components of the famous medicinal plant, Centella Asiatica, aka Gotu Kola. It has well established wound healing and antioxidant activities.
In-vitro (made in the lab) studies also show that Asiaticoside stimulates GAGs (glycosaminoglycans - polysaccharides that are part of the liquidy stuff between our skin cells) production as well as collagen I synthesis. Read more at Gotu Kola >>
One of the biologically active components of Gotu Kola. It's a bit less prominent than its sister component, Asiaticoside, but in-vitro (made in the lab) studies show that Asiatic Acid also stimulates GAGs (glycosaminoglycans - polysaccharides that are part of the liquidy stuff between our skin cells) production as well as collagen I synthesis.
English translation equals that it probably contributes to the well-established moisturizing and wound healing abilities of Gotu Kola.
A super common and cheap fragrance ingredient. It's in many plants, e.g. rosemary, eucalyptus, lavender, lemongrass, peppermint and it's the main component (about 50-90%) of the peel oil of citrus fruits.
It does smell nice but the problem is that it oxidizes on air exposure and the resulting stuff is not good for the skin. Oxidized limonene can cause allergic contact dermatitis and counts as a frequent skin sensitizer.
Limonene's nr1 function is definitely being a fragrance component, but there are several studies showing that it's also a penetration enhancer, mainly for oil-loving components.
All in all, limonene has some pros and cons, but - especially if your skin is sensitive - the cons probably outweigh the pros.
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| what‑it‑does | skin-identical ingredient | moisturizer/humectant |
| irritancy, com. | 0, 0 |
| what‑it‑does | moisturizer/humectant | solvent |
| irritancy, com. | 0, 1 |
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| what‑it‑does | emulsifying | surfactant/cleansing |
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| what‑it‑does | perfuming |
| what‑it‑does | perfuming |
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| irritancy, com. | 0, 1 |
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| what‑it‑does | antimicrobial/antibacterial | perfuming |
| what‑it‑does | skin-identical ingredient | moisturizer/humectant |
| irritancy, com. | 0, 0 |
| what‑it‑does | antioxidant |
| irritancy, com. | 0-3, 0-3 |
| what‑it‑does | moisturizer/humectant | emollient |
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| what‑it‑does | moisturizer/humectant |
| what‑it‑does | soothing | antioxidant | moisturizer/humectant |
| what‑it‑does | skin-identical ingredient |
| what‑it‑does | skin-identical ingredient |
| what‑it‑does | skin-identical ingredient | moisturizer/humectant |
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