What Is Thioglycolic Acid?
Thioglycolic acid, also called mercaptoacetic acid, is a small sulfur-containing molecule that belongs to the group of organic acids known as thiols. It is usually made in a lab by reacting chloroacetic acid with sodium hydrosulfide, then purifying the result to create a clear liquid with a sharp smell. Chemists first noted its strong reducing power in the 1940s and soon explored it for reshaping hair, which led to its early use in permanent wave solutions. Over time formulators found that the same chemical qualities could remove hair and protect products from oxidation, so its role grew within the beauty industry.
Today thioglycolic acid appears in several topical products. You will most often find it in hair-removal creams, permanent wave lotions, chemical hair straighteners, cuticle removers and select antioxidant serums designed to keep formulas stable. While niche, it remains a workhorse wherever strong yet controllable reduction is needed.
Thioglycolic Acid’s Cosmetic Benefits/Uses
This ingredient serves more than one purpose in beauty care
- Antioxidant – helps slow down the breakdown of a formula by neutralizing oxygen that can cause color or scent changes, so the product stays fresh longer
- Depilatory – breaks the disulfide bonds in keratin so unwanted hair softens and wipes away easily, giving smooth skin without shaving
- Hair Waving or Straightening – reshapes the internal bonds of hair strands, allowing stylists to create curls or leave the hair flatter and straighter until the next growth cycle
- Reducing agent – provides strong yet predictable reduction during chemical processes, which can improve the performance of other active ingredients or adjust pH for better product stability
Who Can Use Thioglycolic Acid
Products containing thioglycolic acid are generally formulated for normal, combination or oily skin and for people looking to remove hair or reshape it. Dry or sensitive skin can still use it, but the strong reducing action may sting or over-dry if the product is left on too long, so extra caution is needed. Those with eczema, open cuts or an impaired skin barrier should avoid it until the skin is fully healed.
The ingredient is synthesized in a lab from simple chemicals rather than animal by-products, so it is typically suitable for vegans and vegetarians. Always check the complete ingredient list, as some finished formulas may include additional animal-derived additives such as keratin or collagen.
No formal studies have proved thioglycolic acid unsafe in pregnancy or while breastfeeding, yet data are limited. Absorption through intact skin appears low but the ingredient is potent, so this is not medical advice and anyone who is pregnant or nursing should ask a doctor before using products that contain it.
Thioglycolic acid does not increase the skin’s sensitivity to sunlight the way alpha hydroxy acids can. Nevertheless, many depilatory or hair-removal routines leave the skin temporarily delicate, so wearing broad-spectrum sunscreen afterward is still wise. Keep in mind that most products with thioglycolic acid are rinse-off treatments rather than leave-ons, so contact time is short and use instructions must be followed exactly.
Potential Side Effects/Adverse Reactions
Reactions to topical thioglycolic acid differ from person to person. The points below outline potential side effects, yet most consumers will not experience them when the ingredient is correctly formulated and used as directed.
- Skin irritation including redness stinging or burning
- Chemical burns if the product is left on longer than advised
- Allergic contact dermatitis marked by swelling itching or rash
- Temporary changes in skin color such as light or dark spots
- Unpleasant sulfur-like odor that may linger on skin or hair
- Hair weakening or breakage when overprocessed during waving or straightening
- Nail plate thinning or irritation when used in cuticle removers
- Eye irritation or watering if fumes or splashes reach the eyes
- Respiratory discomfort when inhaling concentrated vapors during salon treatments
If any adverse effect occurs stop using the product immediately rinse the area with plenty of water and seek medical advice if symptoms do not quickly improve.
Comedogenic Rating
Rating: 0. Thioglycolic acid is highly water-soluble, does not leave an oily film and is mostly used in rinse-off formulas. These factors mean it has virtually no ability to block pores, so it earns a non-comedogenic score.
People who are prone to acne or breakouts can generally use products with thioglycolic acid without worrying about added congestion.
Because this ingredient is usually washed off within minutes, any tiny residue left behind is unlikely to sit on the skin long enough to cause issues.
Summary
Thioglycolic acid acts as an antioxidant, a depilatory, a hair waving or straightening agent and a general reducing agent. It neutralizes oxygen to keep formulas fresh, breaks the disulfide bonds in keratin so hair can be removed or reshaped and donates electrons in chemical reactions that improve product stability.
While not a household name, it is a staple in depilatory creams, permanent wave lotions and some niche antioxidant blends. Its strong smell and potent action limit its use in everyday facial care but where it fits, it works hard.
When used as directed the ingredient is considered safe, though misuse can lead to irritation. Anyone trying a new product that contains thioglycolic acid should still perform a small patch test first to make sure their skin agrees with it.