An A-Z Glossary of Every Popular Skin-Care Ingredient to Know

Innovative, efficacious skin-care ingredients are popping up regularly, but there are a handful of mainstays that are called out in formulations over and over again. Just like food recipes, skin-care products are made with different ingredients. Each serves a specific purpose — hyaluronic acid plumps, glycerin moisturizers, salicylic acid fights acne, and vitamin C brightens — and plays a crucial role in the overall formulation of the product. More so than any other category of beauty, skin care is very technical, which is great for results but occasionally tricky to understand if you're not well-versed in all of the ingredients and their respective benefits. That's why we've made a glossary of terms that every skin-care enthusiast should know.

If you've ever found yourself muttering, what on earth is niacinamide? or questioning the difference between AHAs and BHAs, you'll find the information ahead helpful. Consider it your dictionary for all things skin-care ingredients. The world of skin care is a complex one, but with this terminology in your vocabulary, it's about to get a whole lot easier.

Read on for a full glossary that will help you help you remember what common ingredients such as salicylic acid, retinol, and vitamin C do for the skin.

Alpha hydroxy acids, abbreviated as AHAs, are a category of exfoliating acids that are water-soluble and come from animal or plant products (such as sugar, milk, and fruit). Examples of AHAs include glycolic acid, lactic acid, malic acid, citric acid, tartaric acid, and mandelic acid. They increase cell turnover and stimulate collagen production, giving you brighter, smoother skin.

Amino acids are organic compounds, which are a crucial part of the body's natural functions. Amino acids hydrate, reduce inflammation, promote collagen growth, repair damaged skin cells, minimize signs of aging, and more. Peptides are an example of amino acids.

Antioxidants are molecules that help neutralize cell-damaging free radicals in your body (aka unstable molecules). Examples of antioxidants include vitamins A, C, and E, ferulic acid, and niacinamide. They help combat free radicals both internally and externally from environmental factors like smoke and pollution.

Azelaic acid, which comes from grains and wheat, is a naturally occurring ingredient from the dicarboxylid acid family. Its benefits include anti-inflammatory and antibacterial properties, making it great for acne and rosacea. It doesn't exfoliate the skin like most skin-care acids, but it does help treat discoloration in the skin.

Bakuchiol — or phyto-retinol, as it's occasionally called — is a botanical extract with similar benefits to retinol. The major difference between the two ingredients is bakuchiol is gentler and therefore often preferred by those with sensitive skin. The plant alternative also has anti-inflammatory and antioxidant properties.

Benzoyl peroxide is a popular acne-fighting ingredient that attacks breakout-causing bacteria deep in your pores. While it also provides your skin with some exfoliation, it's mainly touted for its ability to treat and prevent acne.

Beta hydroxy acids, aka BHAs, are oil-soluble exfoliating acids that break down dirt, bacteria, and oil deep in pores, making them great for treating acne. In addition to the most popular example, salicylic acid, beta hydroxybutanoic acid, tropic acid, and trethocanic acid are also BHAs.

Ceramides are lipids, which are molecules that make up the function of living cells. They're the key to healthy, hydrated skin, as ceramides help heal and protect your skin barrier. When the skin barrier is damaged, you can experience redness, irritation, dehydration, and discomfort. Additionally, ceramides help your skin look younger and feel smoother and softer.

Citric acid is derived from citrus fruits, like lemons and limes. It's a member of the AHA group and is great for unclogging pores, fading hyperpigmentation, and hydrating the skin.

Ectoin is typically used as an emollient in skin-care formulations and has hydrating properties. It can be synthetic or naturally derived.

Exosomes are derived from human stem cells and can be used two different ways: in skin-care products or injected directly into the skin. They are still in the early stages of being studied but are great for hair loss and antiaging.

Ferulic acid, which comes from oats, apples, brown rice, and oranges, is an antioxidant. Because of this, it helps protect the skin against pollution and UV damage. It's also good for increasing the skin's firmness and elasticity, reducing inflammation, and brightening dark spots.

Glycerin is a great ingredient for hydrating your complexion, as it's a humectant (meaning it attracts water from the air) that traps moisture into the skin. It's a natural compound derived from vegetable oil and animal fats, and it's great for nourishing your skin barrier.

Glycolic acid is an example of an alpha hydroxy acid. Because of its small molecule size, it's able to penetrate the skin deeper than other AHAs, making it effective at resurfacing the skin, treating acne scarring and discoloration, and reducing signs of aging.

Hyaluronic acid is a molecule that holds 1,000 times its weight in water. It's a naturally occurring substance in our bodies — specifically our joints and skin — that acts as a vehicle for hydrating and is great for wound healing and plumping the skin.

As its name suggests, lactic acid is derived from milk and is a member of the alpha hydroxy acids family. It's gentler than glycolic acid due to its larger molecule size, but it packs similar benefits such as resurfacing the top layer of the skin, unclogging pores, and sealing in moisture.

Malic acid of the AHA family is an exfoliating ingredient that promotes cell turnover, thereby brightening the skin and treating acne. It doesn't penetrate the skin as deep as other AHAs, making it more easily tolerated by those with sensitive skin types.

Like malic acid, mandelic acid is another AHA that exfoliates the surface of the skin — except this acid comes from almonds. It brightens uneven skin tone and smooths rough texture by shedding dead skin cells.

Niacinamide, also known as nicotinamide, is a form of vitamin B-3 — an essential nutrient for your body. It can be found naturally in animal products or in plant-based products, like seeds and leafy greens, as nicotinic acid. Niacinamide's skin-care benefits include fighting inflammation, reducing redness, retaining moisture in the skin, increasing natural lipids on the skin, reducing the appearance of pores, reducing excessive oil production, fighting breakouts, smoothing uneven texture, and brightening tone.

Oxybenzone is an active ingredient commonly found in chemical sunscreens that's absorbed into the skin to filter out UV rays. Despite being FDA-approved, the chemical is controversial due to research that indicates it can disrupt hormone levels in animals and damage coral reefs.

Peptides, also known as polypeptides, are short chains of amino acids, the building blocks of proteins like collagen, elastin, and keratin in the skin. In skin care, peptides are a superhero ingredient with a long list of benefits, including anti-aging, wound healing, and anti-inflammatory properties.

Polyglutamic acid is classified as a peptide. It's a natural, biodegradable polymer produced by fermentation. It's made up of a chain of a particular type of amino acid called glutamic acid and is good for locking in moisture in the skin.

Retinol, otherwise known as vitamin A, is a beloved skin-care ingredient that does it all: lightens dark spots and hyperpigmentation, treats acne, smooths fine lines, improves skin's elasticity, exfoliates, and prevents early signs of aging. You can get retinol over-the-counter or via a prescription in higher concentrations. Because of how potent it is, it can cause some irritation when you first begin using it.

Salicylic acid, which is a BHA, is a gentle exfoliating ingredient derived from willow bark, commonly used to fight acne. It has anti-inflammatory and antibacterial properties and is great for resurfacing, leaving skin looking smooth, bright, clear, and more even.

Squalane is an oil that's clear, odorless, and noncomedogenic. It comes from wheat germ, palm treats, and olives. It's great for treating dry patches and eczema, and it boasts an ability to soothe, hydrate, and provide antioxidants to the skin.

Succinic acid is a skin-care acid in its own category outside of the two main groups of acids, alpha hydroxy acids and beta hydroxy acids. Derived from amber and sugar cane, it has antimicrobial properties, as well as antioxidant properties, and can reduce oil production, treat acne, and minimize fine lines.

Tartaric acid is from the alpha hydroxy acid family — it's derived from fruits such as grapes, bananas, and citrus. In addition to exfoliating the skin, its benefits include moisturizing, promoting healing, and minimizing signs of aging.

The use of tranexamic acid started as a prescription medication that mimicked the body's natural amino acid lysine. Now, it's used as a treatment for pigmentation and brightening skin.

Vitamin C is a favorite in the skin-care world thanks to its ability to brighten hyperpigmentation, stimulate collagen, and provide antioxidants to the skin. The vitamin, which can be found in a variety of fruits and vegetables, protects against environmental aggressors like UV rays and pollution.