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Kiehl’s Leave InIngredients 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.
There is definitely some craze going on for coconut oil both in the healthy eating space (often claimed to be the healthiest oil to cook with but this is a topic for another site) and in the skin and hair care space.
We will talk here about the latter two and see why we might want to smear it all over ourselves. Chemically speaking, coconut oil has a unique fatty acid profile. Unlike many plant oils that mostly contain unsaturated fatty acids (fatty acids with double bonds and kinky structure such as linoleic or oleic), coconut oil is mostly saturated (fatty acids with single bonds only) and its most important fatty acid is Lauric Acid (about 50%). Saturated fatty acids have a linear structure that can stack nice and tight and hence they are normally solid at room temperature. Coconut oil melts around 25 °C so it is solid in the tub but melts on contact with the skin.
The saturated nature of coconut oil also means that it is a heavy-duty-oil ideal for dry skin types. A double-blind research confirmed that extra virgin coconut oil is as effective in treating xerosis (aka very dry skin) as mineral oil. Another study found that coconut oil is more effective than mineral oil in treating mild to moderate atopic dermatitis (aka eczema) in children.
So when it comes to dry skin, coconut oil is a goodie, no question there. The question is if it is good or bad for acne-prone skin. Its main fatty acid, Lauric Acid has some research showing that it is a promising ingredient against evil acne-causing bacteria, P. acnes but at the same time, both Lauric Acid and coconut oil have a very high comedogenic rating (4 out of 5). Though comedogenic ratings are not very reliable, anecdotal evidence (i.e. people commenting in forums) shows that people have mixed experiences. While some claim that it worked wonders on their acne others say that it gave them serious blackheads and zits. Try it at your own risk.
As for hair care, coconut oil has pretty solid research showing that it can penetrate into the hair very well (better than mineral oil and sunflower oil) and it can prevent hair protein loss as well as combing damage. If you have problems with damaged hair, split ends, coconut oil is worth trying as a pre- or/and post-wash treatment. Labmuffin has an awesome blogpost explaining in more detail why coconut oil is good for your hair.
A couple of other things worth mentioning: coconut oil might help with wound healing (promising animal study), it has some antifungal activity (against dermatophytes that cause the thing known as ringworm) and it also works as an insect repellent against black flies.
Overall, coconut oil is definitely a goodie for the hair and dry skin. If that warrants for the magic oil status it enjoys, we don't know.
A modified dimethicone-type silicone molecule that also contains amino-groups. Having amino-groups means that Amodimethicone also has Nitrogen in its molecule that likes to have a positive charge. Positively charged (or quaternised) molecules are substantive to skin and hair as those are negatively charged surfaces and are excellent film formers. Amodiemthcone is no exception and it is especially recommended for hair-care products for its long-lasting hair conditioning benefits.
A cationic polymer molecule (a big molecule with repeated subunits and a positive charge) that acts both as a film-former and conditioning ingredient as well as a thickening agent.
Propylene Glycol Dicaprylate/Dicaprate is an emollient that leaves a light, non-oily smooth and velvet skin sensation. According to manufacturer info it's also great at dispersing and dissolving pigments and sunscreen actives. Most often you will meet this guy in light moisturizers, sunscreens or makeup products.
We don't have description for this ingredient yet.
It’s pretty much the current IT-preservative. It’s safe and gentle, but even more importantly, it’s not a feared-by-everyone-mostly-without-scientific-reason paraben.
It’s not something new: it was introduced around 1950 and today it can be used up to 1% worldwide. It can be found in nature - in green tea - but the version used in cosmetics is synthetic.
Other than having a good safety profile and being quite gentle to the skin it has some other advantages too. It can be used in many types of formulations as it has great thermal stability (can be heated up to 85°C) and works on a wide range of pH levels (ph 3-10).
It’s often used together with ethylhexylglycerin as it nicely improves the preservative activity of phenoxyethanol.
Exactly what it sounds: nice smelling stuff put into cosmetic products so that the end product also smells nice. Fragrance in the US and parfum in the EU is a generic term on the ingredient list that is made up of 30 to 50 chemicals on average (but it can have as much as 200 components!).
If you are someone who likes to know what you put on your face then fragrance is not your best friend - there's no way to know what’s really in it.
Also, if your skin is sensitive, fragrance is again not your best friend. It’s the number one cause of contact allergy to cosmetics. It’s definitely a smart thing to avoid with sensitive skin (and fragrance of any type - natural is just as allergic as synthetic, if not worse!).
We don't have description for this ingredient yet.
We don't have description for this ingredient yet.
We don't have description for this ingredient yet.
We don't have description for this ingredient yet.
We don't have description for this ingredient yet.
We don't have description for this ingredient yet.
We don't have description for this ingredient yet.
You probably know olive oil from the kitchen as a great and healthy option for salad dressing but it's also a great and healthy option to moisturize and nourish the skin, especially if it's on the dry side.
Similar to other emollient plant oils, it's loaded with nourishing fatty acids: oleic is the main component (55-83%), and also contains linoleic (3.5-20%) and palmitic acids (7-20%). It also contains antioxidant polyphenols, tocopherols (types of vitamin E) and carotenoids and it's one of the best plant sources of skin-identical emollient, Squalene.
Overall, a great option for dry skin but less so for acne-prone or damaged skin.
The oil coming from the seeds of the Moringa tree, a big white-flowered tree native to India. It's a yellow oil similar to olive oil. It's rich in nourishing and moisturizing fatty acid, oleic (75%) and also contains behenic acid (up to 8%) that makes moringa very stable and gives the oil a long shelf life.
It blends easily with essential oils and can also help to stabilize scents so it's a popular oil in the perfume industry.
Linalool is a super common fragrance ingredient. It’s kind of everywhere - both in plants and in cosmetic products. It’s part of 200 natural oils including lavender, ylang-ylang, bergamot, jasmine, geranium and it can be found in 90-95% of prestige perfumes on the market.
The problem with linalool is, that just like limonene it oxidises on air exposure and becomes allergenic. That’s why a product containing linalool that has been opened for several months is more likely to be allergenic than a fresh one.
A study made in the UK with 483 people tested the allergic reaction to 3% oxidised linalool and 2.3% had positive test results.
We don't have description for this ingredient yet.
The unfancy name for it is lye. It’s a solid white stuff that’s very alkaline and used in small amounts to adjust the pH of the product and make it just right.
For example, in case of AHA or BHA exfoliants, the right pH is super-duper important, and pH adjusters like sodium hydroxide are needed.
BTW, lye is not something new. It was already used by ancient Egyptians to help oil and fat magically turn into something else. Can you guess what? Yes, it’s soap. It still often shows up in the ingredient list of soaps and other cleansers.
Sodium hydroxide in itself is a potent skin irritant, but once it's reacted (as it is usually in skin care products, like exfoliants) it is totally harmless.
Geraniol is a common fragrance ingredient. It smells like rose and can be found in rose oil or in small quantities in geranium, lemon and many other essential oils.
Just like other similar fragrance ingredients (like linalool and limonene) geraniol also oxidises on air exposure and becomes allergenic. Best to avoid if you have sensitive skin.
The caramel in cosmetics is pretty much the same one that you know from the kitchen. It is derived by controlled heat treatment of food-grade carbohydrates (sugars) and works as a brown colorant.
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).
We don't have description for this ingredient yet.
Citronellol is a very common fragrance ingredient with a nice rose-like odor. In the UK, it’s actually the third most often listed perfume on the ingredient lists.
It can be naturally found in geranium oil (about 30%) or rose oil (about 25%).
As with all fragrance ingredients, citronellol can also cause allergic contact dermatitis and should be avoided if you have perfume allergy. In a 2001 worldwide study with 178 people with known sensitization to fragrances citronellol tested positive in 5.6% of the cases.
There is no known anti-aging or positive skin benefits of the ingredient. It’s in our products to make it smell nice.
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.
It's one of those things that help your cosmetics not to go wrong too soon, aka a preservative. It can be naturally found in fruits and teas but can also be made synthetically.
No matter the origin, in small amounts (up to 1%) it’s a nice, gentle preservative. Has to be combined with some other nice preservatives, like potassium sorbate to be broad spectrum enough.
In high amounts, it can be a skin irritant, but don’t worry, it’s never used in high amounts.
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| what‑it‑does | solvent |
| what‑it‑does | emollient | perfuming |
| irritancy, com. | 0, 4 |
| what‑it‑does | emollient |
| what‑it‑does | viscosity controlling |
| what‑it‑does | emollient |
| irritancy, com. | 0, 1 |
| what‑it‑does | emulsifying | surfactant/cleansing |
| irritancy, com. | 2, 4 |
| what‑it‑does | preservative |
| what‑it‑does | perfuming |
| what‑it‑does | moisturizer/humectant | surfactant/cleansing | viscosity controlling |
| what‑it‑does | moisturizer/humectant |
| what‑it‑does | surfactant/cleansing | emulsifying | surfactant/cleansing |
| what‑it‑does | surfactant/cleansing |
| what‑it‑does | preservative |
| what‑it‑does | emulsifying | surfactant/cleansing |
| what‑it‑does | antioxidant | emollient |
| irritancy, com. | 0, 0-2 |
| what‑it‑does | emollient |
| what‑it‑does | perfuming |
| what‑it‑does | antimicrobial/antibacterial | emulsifying | preservative | surfactant/cleansing |
| what‑it‑does | buffering |
| what‑it‑does | perfuming |
| what‑it‑does | colorant |
| what‑it‑does | skin-identical ingredient | moisturizer/humectant |
| irritancy, com. | 0, 0 |
| what‑it‑does | perfuming |
| what‑it‑does | perfuming | solvent |
| what‑it‑does | preservative | perfuming | solvent | viscosity controlling |