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Kiehl’s Vital Skin-Strengthening Super Serum

Vital Skin-Strengthening Super Serum

Our skin-strengthening serum penetrates skin up to 8 surface layers deep* and helps target the appearance of visible signs of ageing by helping to diminish the look of fine lines and reviving tired-looking, dull skin, which can be caused by daily stressors. Formulated with 11kDa (Kilodalton) Hyaluronic Acid—our smallest form of Hyaluronic Acid—and with Herbal Adaptogens. Our potent “super serum” penetrates skin’s surface layers and helps fortify skin barrier function. Skin feels suppler, more resilient, and looks younger.
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Skim through

Ingredient name what-it-does irr., com. ID-Rating
Aqua/Water solvent
Dimethicone emollient 0, 1
Glycerin skin-identical ingredient, moisturizer/​humectant 0, 0 superstar
Alcohol Denat antimicrobial/​antibacterial, solvent, viscosity controlling icky
Hamamelis Virginiana Water/Witch Hazel Water soothing goodie
Propanediol solvent, moisturizer/​humectant
Phenoxyethanol preservative
Tocopherol antioxidant 0-3, 0-3 goodie
Ammonium Polyacryloyldimethyl Taurate viscosity controlling
Schisandra Chinensis Fruit Extract
Capryloyl Salicylic Acid exfoliant goodie
Caprylyl Glycol moisturizer/​humectant, emollient
Xanthan Gum viscosity controlling
PEG-60 Hydrogenated Castor Oil emulsifying, surfactant/​cleansing
Panax Ginseng Root Extract antioxidant, emollient goodie
Sodium Acetylated Hyaluronate moisturizer/​humectant goodie
PEG-20 Methyl Glucose Sesquistearate emulsifying
Disodium EDTA chelating
Ocimum Sanctum Leaf Extract
Citrus Aurantium Dulcis Peel Oil/Orange Peel Oil perfuming icky
Limonene perfuming, solvent icky
Adenosine cell-communicating ingredient goodie
Sodium Hydroxide buffering
Methyldihydrojasmonate
Citric Acid buffering
Eugenol perfuming icky
Sodium Benzoate preservative
Pelargonium Graveolens Flower Oil perfuming icky
Citral perfuming icky
Potassium Sorbate preservative
Lavandula Angustifolia Oil/Lavender Oil antimicrobial/​antibacterial, perfuming icky
Cymbopogon Schoenanthus Oil
Citronellol perfuming icky
Linalool perfuming icky
Geraniol perfuming icky
Rosmarinus Officinalis Leaf Oil/Rosemary Leaf Oil antioxidant, antimicrobial/​antibacterial icky

Kiehl’s Vital Skin-Strengthening Super Serum
Ingredients explained

Also-called: Aqua;Water | What-it-does: solvent

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. 

What-it-does: emollient | Irritancy: 0 | Comedogenicity: 1

Probably the most common silicone of all. It is a polymer (created from repeating subunits) molecule and has different molecular weight and thus different viscosity versions from water-light to thick liquid.

As for skincare, it makes the skin silky smooth, creates a subtle gloss and forms a protective barrier (aka occlusive). Also, works well to fill in fine lines and wrinkles and give skin a plump look (of course that is only temporary, but still, it's nice). There are also scar treatment gels out there using dimethicone as their base ingredient. It helps to soften scars and increase their elasticity. 

Glycerin - superstar
Also-called: Glycerol | What-it-does: skin-identical ingredient, moisturizer/humectant | Irritancy: 0 | Comedogenicity: 0
  • 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
Read all the geeky details about Glycerin here >>

  • It's a super common and super debated skincare ingredient
  • It has several benefits: great solvent, penetration enhancer, creates cosmetically elegant, light formulas, great astringent and antimicrobial
  • It can be very drying if it's in the first few ingredients on an ingredient list
  • Some experts even think that regular exposure to alcohol damages skin barrier and causes inflammation though it's a debated opinion (read more in geeky details tab)
Read all the geeky details about Alcohol Denat. here >>

What-it-does: soothing, astringent

The distillate created from different parts of the hazelnut-bush-like magic tree, commonly called Witch Hazel. Hamamelis Virginiana Water is a bit of a sloppy ingredient name as the leaves, the twigs and the bark can be used to create extracts or distillates and the different parts contain different amounts of biologically active components. But what you are getting is probably a nice water with astringent, soothing, antioxidant and antibacterial magic properties.  

We went into great detail about Witch Hazel in cosmetics here, detailing the main biologically active components and how they are different in different parts of the plant. Click here and read more >>

Also-called: Zemea | What-it-does: solvent, moisturizer/humectant

Propanediol is a natural alternative for the often used and often bad-mouthed propylene glycol. It's produced sustainably from corn sugar and it's Ecocert approved. 

It's quite a multi-tasker: can be used to improve skin moisturization, as a solvent, to boost preservative efficacy or to influence the sensory properties of the end formula. 

What-it-does: preservative

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. 

Tocopherol - goodie
Also-called: Vitamin E | What-it-does: antioxidant | Irritancy: 0-3 | Comedogenicity: 0-3
  • 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
Read all the geeky details about Tocopherol here >>

There is not much info about this guy in itself other than it helps to thicken up products and stabilize oil-in-water emulsions. It usually comes to the formula as part of some thickener complex. For example, coupled with isohexadecane and polysorbate 80, the trio forms an instant gel upon mixing with water. 

We don't have description for this ingredient yet.

Also-called: LHA | What-it-does: exfoliant

We don't have description for this ingredient yet.

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 one of the most commonly used thickeners and emulsion stabilizers. If the product is too runny, a little xanthan gum will make it more gel-like. Used alone, it can make the formula sticky and it is a good team player so it is usually combined with other thickeners and so-called rheology modifiers (helper ingredients that adjust the flow and thus the feel of the formula). The typical use level of Xantha Gum is below 1%, it is usually in the 0.1-0.5% range. 

Btw, Xanthan gum is all natural, a chain of sugar molecules (polysaccharide) produced from individual sugar molecules (glucose and sucrose) via fermentation. It’s approved by Ecocert and also used in the food industry (E415). 

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.

Also-called: True Ginseng, Ginseng, Korean Ginseng | What-it-does: antioxidant, emollient

A  traditional Korean medicine used for more than 2000 years. Regarding skin care, its main thing seems to be enhancing skin nutrition and metabolism as a result of improving blood circulation.

It also contains biologically active components referred to as ginseng saponins (ginsenosides) that have potent antioxidant properties

What-it-does: moisturizer/humectant

Sodium Acetylated Hyaluronate is a variation of current IT moisturizer, Hyaluronic acid, where some water-loving -OH groups are replaced by amphipathic (partly water-loving and partly water-hating) acetyl groups. The modified molecule is claimed to have even better moisture retention ability than normal HA and better affinity to the skin surface. 

The better affinity comes from the acetyl groups that act as tiny "anchors" to attach the HA molecule to the skin. Staying on top of the skin better and longer means longer-lasting surface hydration and improved elasticity. It is also less sticky and more cosmetically elegant than normal HA, so no wonder the nickname of this molecule is super hyaluronic acid. 

What-it-does: emulsifying

A mild, water-loving emulsifier that's safe for sensitive skin or eye-care formulations. It helps to create low viscosity oil-in-water emulsions, ideal for milks, serums, and sprayable formulations. It's derived from natural sources and  gives a light, satiny afterfeel.    

What-it-does: chelating

Super common little helper ingredient that helps products to remain nice and stable for a longer time. It does so by neutralizing the metal ions in the formula (that usually get into there from water) that would otherwise cause some not so nice changes.

It is typically used in tiny amounts, around 0.1% or less.

We don't have description for this ingredient yet.

Also-called: Sweet Orange Peel Oil, Citrus Sinensis Oil;Citrus Aurantium Dulcis Peel Oil | What-it-does: perfuming

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.  

Limonene - icky
What-it-does: perfuming, solvent, deodorant

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

Adenosine - goodie

Adenosine is an important little compound in our body that has a vital cell-signalling role. Research on smearing it on our face is also promising and shows so far a couple of things:

  • It can help with wound healing
  • It’s a good anti-inflammatory agent
  • It might even help with skin’s own collagen production and improve skin firmness and elasticity
  • It helps with barrier repair and protection
  • It might be even useful for the hair helping with hair thickness and hair growth
Also-called: lye | What-it-does: buffering

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.  

We don't have description for this ingredient yet.

What-it-does: buffering

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. 

Eugenol - icky
What-it-does: perfuming

A colorless or yellowish oil that's used as a fragrance. It has a spicy scent and can be found for example in basil, clove or cinnamon oil.

A 2006 in-vitro  (made in the lab not on real people) study examined if clove oil is cytotoxic and found that not only clove oil but also its main constituent, eugenol is cytotoxic even at very low concentration (0.03%). It’s also one of the “EU 26 fragrances” that has to be labelled separately (and cannot be simply included in the term “fragrance/perfume” on the label) because of allergen potential. Best to avoid at least in leave-on products.

What-it-does: preservative

A helper ingredient that helps to make the products stay nice longer, aka preservative. It works mainly against fungi. 

It’s pH dependent and works best at acidic pH levels (3-5). It’s not strong enough to be used in itself so it’s always combined with something else, often with potassium sorbate.

Also-called: Rose Geranium Flower Essential Oil | What-it-does: perfuming

The fragrant essential oil coming from the flowers of Rose Geranium. Like most essential oils, it contains antioxidant and antimicrobial components, but the main ones are fragrant constituents (like citronellol and geraniol). Be careful with it, if your skin is sensitive. 

Citral - icky
What-it-does: perfuming

It’s a common fragrance ingredient that smells like lemon and has a bittersweet taste.  It can be found in many plant oils, e.g. lemon, orange, lime or lemongrass. 

It’s one of the “EU 26 fragrances” that has to be labelled separately (and cannot be simply included in the term “fragrance/perfume” on the label) because of allergen potential. Best to avoid if your skin is sensitive.

What-it-does: preservative

It's one of those things that help your cosmetics not to go wrong too soon, aka a preservative. It’s not a strong one and doesn’t really work against bacteria, but more against mold and yeast. To do that it has to break down to its active form, sorbic acid. For that to happen, there has to be water in the product and the right pH value (pH 3-4). 

But even if everything is right, it’s not enough on its own. If you see potassium sorbate you should see some other preservative next to it too.

Also-called: Lavender Essential Oil;Lavandula Angustifolia Oil | What-it-does: antimicrobial/antibacterial, perfuming

We have to start by writing how fascinated we are by the amazing lavender fields of Provance and we do love pretty much everything about lavender: its look, its color, its scent.... but, when it comes to skincare, lavender is a questionable ingredient that you probably do not want in your skincare products.

First, let us start with the pros: it has a lovely scent, so no wonder that it is popular as a fragrance ingredient in natural products wanting to be free from synthetic fragrances but still wanting to smell nice. The scent of lavender is famous for having calming and relaxing properties and some smallish scientific studies do support that. Inhaled volatile compounds seem to have a soothing effect on the central nervous system and studies have shown that lavender aromatherapy can improve patient's anxiety and experience in hospitals.   

Also-called: Lemon Grass Oil

We don't have description for this ingredient yet.

What-it-does: perfuming

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%). 

Linalool - icky
What-it-does: perfuming, deodorant

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.

Geraniol - icky
What-it-does: perfuming

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.

Also-called: Rosemary Leaf Oil;Rosmarinus Officinalis Leaf Oil | What-it-does: antioxidant, antimicrobial/antibacterial

The essential oil coming from the leafs of the lovely herb, rosemary. It contains several fragrant components, including the well-known irritant, camphor (around 15%). It has a nice smell, is a potent antioxidant and it's also an antimicrobial agent.

If your skin is sensitive, it's probably a good idea to avoid it.

You may also want to take a look at...

what‑it‑does solvent
Normal (well kind of - it's purified and deionized) water. Usually the main solvent in cosmetic products. [more]
what‑it‑does emollient
irritancy, com. 0, 1
A very common silicone that gives both skin and hair a silky smooth feel. It also forms a protective barrier on the skin and fills in fine lines. Also used for scar treatment. [more]
what‑it‑does skin-identical ingredient | moisturizer/humectant
irritancy, com. 0, 0
A real oldie but a goodie. Great natural moisturizer and skin-identical ingredient that plays an important role in skin hydration and general skin health. [more]
what‑it‑does antimicrobial/antibacterial | solvent | viscosity controlling
Alcohol with some additives to make it unconsumable. It is great solvent, penetration enhancer, creates cosmetically elegant, light formulas, great astringent, and antimicrobial. In large amounts, it can be very drying to the skin. [more]
what‑it‑does soothing
The distillate created from the hazelnut-bush-like magic tree, commonly called Witch Hazel. It might have astringent, soothing, antioxidant and antibacterial properties. [more]
what‑it‑does solvent | moisturizer/humectant
A natural corn sugar derived glycol. It can be used to improve skin moisturization, as a solvent, to boost preservative efficacy or to influence the sensory properties of the end formula. [more]
what‑it‑does preservative
Pretty much the current IT-preservative. It’s safe and gentle, and can be used up to 1% worldwide. [more]
what‑it‑does antioxidant
irritancy, com. 0-3, 0-3
Pure Vitamin E. Great antioxidant that gives significant photoprotection against UVB rays. Works in synergy with Vitamin C. [more]
what‑it‑does viscosity controlling
A polymer that helps to thicken up products and stabilize oil-in-water emulsions. [more]
what‑it‑does exfoliant
what‑it‑does moisturizer/humectant | emollient
A handy multi-tasking ingredient that gives the skin a nice, soft feel and also boosts the effectiveness of other preservatives. [more]
what‑it‑does viscosity controlling
A super commonly used thickener and emulsion stabilizer. [more]
what‑it‑does emulsifying | surfactant/cleansing
A castor oil derived, white, lard-like helper ingredient that is used as a solubilizer to put fragrances into water-based products such as toners.
what‑it‑does antioxidant | emollient
Ginseng - A traditional Korean medicine that has antioxidant properties, and is known to improve blood circulation. [more]
what‑it‑does moisturizer/humectant
Sodium Acetylated Hyaluronate is a variation of current IT moisturizer, Hyaluronic acid, where some water-loving -OH groups are replaced by amphipathic (partly water-loving and partly water-hating) acetyl groups. [more]
what‑it‑does emulsifying
A mild, water-loving emulsifier that's safe for sensitive skin or eye-care formulations. It helps to create low viscosity oil-in-water emulsions. [more]
what‑it‑does chelating
Super common little helper ingredient that helps products to remain nice and stable for a longer time. It does so by neutralizing the metal ions in the formula (that usually get into there from water) that would otherwise cause some not so nice changes. [more]
what‑it‑does perfuming
The essential oil coming from the rind of the orange. Its main component (83-97%) is limonene, the super common fragrant ingredient. [more]
what‑it‑does perfuming | solvent
A super common fragrance ingredient found naturally in many plants including citrus peel oils, rosemary or lavender. It autoxidizes on air exposure and counts as a common skin sensitizer. [more]
what‑it‑does cell-communicating ingredient
An important compound in our body that has a vital cell-signalling role. It is wound healing, anti-inflammatory and can help with barrier repair. [more]
what‑it‑does buffering
Lye - A solid white stuff that’s very alkaline and used in small amount to adjust the pH of the product.  [more]
what‑it‑does buffering
An AHA that comes from citrus fruits. It is usually used as a helper ingredient to adjust the pH of the formula. [more]
what‑it‑does perfuming
A colorless or yellowish oil that's used as a fragrance with a spicy scent. [more]
what‑it‑does preservative
A preservative that works mainly against fungi. Has to be combined with other preservatives. [more]
what‑it‑does perfuming
The essential oil coming from the flowers of Rose Geranium. Like most essential oils, it contains antioxidant and antimicrobial components, but the main ones are fragrant constituents. [more]
what‑it‑does perfuming
A common fragrance ingredient that smells like lemon. [more]
what‑it‑does preservative
A not so strong preservative that doesn’t really work against bacteria, but more against mold and yeast. [more]
what‑it‑does antimicrobial/antibacterial | perfuming
Lavender - essential oil with a calming scent and antimicrobial properties. Contains fragrant components (linalyl acetate - 50% and linalool - 35%) and might be cytotoxic from 0.25%. [more]
what‑it‑does perfuming
A common fragrance ingredient with a nice rose-like smell. [more]
what‑it‑does perfuming
A super common fragrance ingredient that can be found among others in lavender, ylang-ylang, bergamot or jasmine. The downside of it is that it oxidises on air exposure and might become allergenic. [more]
what‑it‑does perfuming
A common fragrance ingredient that smells like rose and can be found in rose oil. [more]
what‑it‑does antioxidant | antimicrobial/antibacterial
The essential oil coming from the leafs of rosemary. It has a nice smell, is a potent antioxidant and it's also an antimicrobial agent. Contains several fragrant components, including potential skin irritant, camphor (around 15%).