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Cosmetics Chemistry: Beauty Ingredients and Their Purposes

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Although trying to figure out what goes into your favorite eye shadow or shampoo can feel like trying to translate a language you’ve never heard before, each ingredient on the list—from aqua to zinc—really does have a purpose and function.

  • Agar, also known as algae, carageenan, laminaria, ulva lactuca, and ascophyllum, contains protein and several vitamins. It’s usually added to moisturizers as an emollient or antioxidant.
  • Alcohol SD-40 is a high-grade cosmetic alcohol that acts as an emollient and a vehicle for the other ingredients. Alcohols (including ethyl alcohol, methyl alcohol, and benzyl alcohol) also help keep the product bacteria-free, but some alcohols can cause dryness and irritation for those with sensitive skin.
  • Allantoin is used in skin creams and lotions and is a by-product of uric acid; it is an effective calming agent that also reduces skin irritation.
  • Aluminum chlorohydrate is one of the most common ingredients in antiperspirant. Technically it’s a salt, and when it reacts with the enzymes in sweat, it forms a temporary “plug” that sits in the pore and prevents more sweat from being released. (The plug is easily washed or sloughed away by bathing.) Aluminum chlorohydrate also acts as an astringent, causing the pores in the underarm to constrict so they can’t release more sweat.
  • Cellulose can refer to any plant-derived matter. In creams and lotions, it is used as a thickener and allows oil ingredients to blend with water without separating.
  • Diethanolomine, like its cousin triethanolomine, sometimes goes by its initials DEA (or TEA, in the case of triethanolomine). It’s a solvent that’s added to cleansers to make them lather and foam.
  • Dimethicone is a form of silicone. Used often in hair products, it makes the product slippery and spreadable. In general, any ingredients with the suffix “cone” are forms of silicone that perform similar functions.
  • Glycerin is found naturally in skin and is added to skin creams to increase hydration.
  • Glycol stearate is a thickener added to products like shampoos to give them a pearly or opalescent look. It doesn’t change how the product works, but it makes it look appealing.
  • Lanolin is a protein derived from sheep’s sweat glands. It’s a high-quality moisturizer that’s especially effective for people with dry or sensitive skin. Chemically, it’s very similar to oil produced by human sebaceous glands.
  • Lecithin, a lipid found naturally in plant and animal cells, is used in moisturizers and skin creams as an emollient and moisturizing agent. It helps protect the outer layers of the epidermis against dryness and irritation, keeping the layers soft and allowing them to repair and regenerate.
  • Mica is a reflective mineral that’s used in makeup products and sometimes toothpaste. It is responsible for shimmer and pearlescence.
  • Panthenol, sometimes called pantothenic acid, is a form of vitamin B5. In hair products, it seals the hair shaft, making strands soft and shiny. It’s sometimes used in skin ointments that treat burns or irritation because it can reduce inflammation and speed healing.
  • Parabens (including butylparaben, methylparaben, etc.) are preservatives. Used widely in up to 70 percent of makeup, skin products, and other cosmetics, they prevent spoilage and inhibit bacteria and fungi.
  • Potassium sorbate inhibits the growth of mold and yeast, and is often used as a preservative.
  • Propylene glycol, like other glycols, is a humectant agent used in skin creams that also helps other ingredients be absorbed more readily. It is not dangerous, as many chain emails or alarmist websites would have you believe. In cosmetics, it is used in very small amounts, and the Department of Health and Human Services has determined that it poses no threat.
  • Sodium hydroxide is the chemical term for lye. This alkaline substance is used to modify a product’s pH balance (i.e., to make it less acidic). Products with large amounts of sodium hydroxide can severely irritate skin.
  • Sodium lauryl sulfate is a surface-active substance used most often in shampoo, but it is also used in skin cleansers. It loosens dirt and oils, making it easier to wash them away. Sodium lauryl sulfate is highly irritating to skin (its cousin sodium laureth sulfate is milder), but contrary to popular belief, it does not cause cancer.
  • Stearyl alcohol is used in emulsions to keep all the ingredients mixed together and suspended properly. It is also an emollient.
  • Talc is one of the primary ingredients in powdered cosmetics like eye shadow and blush. It is an absorbent natural compound that comprises silicon and magnesium.
  • Titanium dioxide is used to thicken and lighten cosmetics like foundation, blush, and eye shadow. It’s also a sunscreen, protecting against both UVA and UVB rays without causing irritation to skin.
  • Tocopherol, along with its chemical cousins tocopherol acetate, tocopheryl linoleate, and tocopheryl nicotinate, is a form of vitamin E. It is added to lipsticks and other emollient cosmetics like concealer or cream blush as an inexpensive but powerful antioxidant.
  • Xanthan gum is a thickening agent that gives products their proper texture.

This is far from an exhaustive list; there are literally thousands of ingredients that can be included in modern cosmetics. Most products contain active ingredients, plant extracts, preservatives, thickeners, emollients, emulsifiers, and also a few fragrance additives and coloring agents. One way to tell the proportion of these ingredients to one another is to see where they fall on the product’s label; the active ingredients and those that exist in large amounts are listed first, and fragrances, dyes, and ingredients that exist only in tiny amounts are listed at the end. Reading cosmetics labels can still feel like deciphering a foreign language, but being able to translate even a few key words and phrases makes everything make a lot more sense. 

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