When I mention acids, some customers show concern. Do you worry about acids on your skin? There are a variety of acids used as ingredients in cosmetic products. But sometimes the term acid brings up negative connotations and people think of an acid as harmful or corrosive. Not all acids are the same though. Acids range from orange juice (citric acid) that is completely safe to drink to muriatic acid (hydrochloric acid) that is used as a floor stripper and can cause severe burns to the skin.
I’m going to explain a little about what an acid is and then go through some common acid ingredients used in cosmetics.
Simply put, an acid is something that has a pH of less than 7 on the pH scale. Anything from 1-7 is an acid, anything from 7-14 is a base or alkaline. Chemically speaking, an acid is a molecule that can donate a proton, or accept an electron. A hydrogen ion is a proton and a pH measurement is related to the amount of free hydrogen ion in a solution.
Acids typically taste sour. Think of yogurt that contains lactic acid. Acids also react with bases to form salts. When the acid becomes a salt, the ending of the word changes from ‘acid’ to ‘ate’. When this salt is dissolved in water, the acid and the base separate again. Acids are strong or weak based on how they separate as salts when dissolved in water. Stronger acids separate easier than weaker acids.
I won’t bore you with how to calculate acid dissociation constants that I stressed over too much in college. Instead, let's talk about some acids that we use in cosmetics and why we use them. I’ve broken them down into six categories. Acids that act as chemical exfoliants are the ones that you need to be careful of as too much can damage the skin. The other cosmetic acids listed below are mild acids and have many skin benefits.
Exfoliants are used on the skin to remove the outer layer of dead skin cells. Stronger acids can sometimes go deeper than the outer, superficial layer of skin which is when you need to be careful. These acids cause deterioration of the bonds that occur between skin cells which causes the cells to separate and then slough off. While low levels of these chemical exfoliants are safe, care must be taken. Higher levels can cause not only skin irritation, but scarring and pigmentation spots. These are the acids that you must be careful of in skin care. There are two types; alpha hydroxy acids and beta hydroxy acids.
Alpha hydroxy acids (AHAs) are found in fruits and include lactic acid, malic acid, citric acid and glycolic acid. These acids can be found in toners, masks and creams. Although AHAs are considered a mild exfoliation treatment, they can still cause skin irritation. We recommend using just low concentrations of AHAs (less than 10%). Citric acid, one of the AHAs, is often used in very low amounts in cosmetics to adjust the pH so that it is balanced with skin. It is completely safe used at these levels.
Beta hydroxy acids (BHAs) are similar to AHAs in use for exfoliation. They are oil soluble, whereas AHAs are water soluble. This makes BHAs more useful for people with oily skin and gives them more ability to clean out pores. The most common BHA is salicylic acid which is found in Willow bark.
Vinegar (acetic acid) is a common household acid. Vinegar bought at the grocery store is typically 4-8% acetic acid. This concentration is still too high to use directly on the skin, but you can dilute it about 1 part vinegar to 3 parts water (or more) and use it on the skin. We use vinegar to extract some of our mineral rich herbs and then use just a small percentage in a product so it is not burning to the skin.
Acid Moisturizers / Humectants
Hyaluronic acid (also known as a glycosaminoglycan) is a naturally occurring component of skin structure. Hyaluronic acid can bind up to 1000 times its weight in water and so it is crucial for maintaining hydration in the skin. It also contributes to skin plumpness and skin elasticity and smooths the skin. All together this results in less visible fine lines and wrinkles in the skin. It is used in rather low concentrations in skin care products and is very safe. This is the same hyaluronic acid that some people get injections of in their damaged joints as well as into their skin.
Pyroglutamic acid (PCA) is a naturally occurring component of skin that helps to hold water in the skin. It is derived from the amino acid glutamic acid and part of the body’s glutathione cycle. You can find PCA in skin products and hair products. It is completely safe. It is also available as a dietary supplement.
Amino Acids are small units that make up proteins. While proteins are too large to penetrate skin, amino acids can penetrate the upper layers of the skin. There, they can help hold moisture in the skin and have other beneficial effects as well. Proline is one amino acid we use in some products to help promote collagen production.
Ascorbic acid (Vitamin C) is not only an important cellular antioxidant, but it is also vital for the skin’s production of collagen fibers. Ascorbic acid can also help reduce hyperpigmentation and brighten skin. Since vitamin C is a very unstable molecule, in cosmetics we use modified forms of vitamin C that have been stabilized as an ester. These include tetrahexyldecyl ascorbate and ascorbyl palmitate. Vitamin C is important to ingest and to use topically.
Alpha Lipoic Acid (ALA) is naturally made in your skin in the cell’s mitochondria. It is important in the conversion of glucose to energy production in the cell. It helps protect your skin from environmental damage and minimizes sign of aging. Because it is good at regenerating other antioxidants it is often referred to as the “universal antioxidant”. This is another antioxidant that is often used as a dietary supplement.
Organic acids are very weak acids that are widely distributed in nature. They include the alpha hydroxy acids mentioned above, but also include caffeic acid, rosmarinic acid, gallic acid and others that are found in herbs. You will not find these names mentioned individually on the label but they are contained in our herb extracts. They act as antioxidants but have other beneficial effects on skin too. They are particularly good for sun damaged skin and to reduce premature aging.
Acids for Whitening / Brightening
Kojic acid is produced by microorganisms used in the fermentation of rice for the production of sake. It is also found in some mushrooms. It inhibits production of the skin pigment, melanin. By doing this it makes an effective whitening/ brightening agent. It can help reduce hyperpigmentation spots caused by sunlight and age. It can be slightly irritating to the skin though.
Acid Fatty acids / Emollients
Fatty acids are a vital component of fats and oils and act as emollients for skin. Some fatty acids include linoleic acid, oleic acid, myristic acid and stearic acid. Most of these you will not see directly written on the label as they are part of triglycerides found in oils including olive oil or sunflower oil as well as butters such as shea butter. All are important for helping to lock moisture into the skin.
Sodium Benzoate / benzoic acid is a preservative used in cosmetics to keep fungus and bacteria from growing.
Potassium sorbate / sorbic acid is a preservative used in cosmetics to keep fungus, yeast and bacteria from growing.
Gluconic acid (Glucono Delta Lactone) is used to help boost preservative activity while also moisturizing.
Preservatives are necessary for a cream or lotion to be safe for the skin because it prevents potentially harmful bacteria and fungi from growing.
This is just a short overview of acids found in cosmetics. But our hope is that with a little chemistry knowledge, acids are less scary.