Ingredient review
Methyl Thioglycolate
INCI: METHYL THIOGLYCOLATE
Methyl thioglycolate is a potent chemical that breaks down hair protein, but it can cause skin irritation and burns if misused.
In plain English
Methyl thioglycolate is a synthetic chemical that works by breaking the bonds in hair protein, making hair easy to remove or reshape. It has a very strong, unpleasant smell (like rotten eggs) and is typically used only in professional salon treatments because it can irritate or burn skin if left on too long. You won't find it in everyday skincare products—it's mainly in depilatory creams and hair-straightening solutions.
Review score
Safety, usefulness, and evidence
Higher-caution ingredient
The evidence base is useful, but some claims depend heavily on the formula.
Main practical flags: irritation is high; clogging risk is low.
- Source
- synthetic
- Evidence
- moderate
- Irritation
- high
- Clogging risk
- low
Quick decision guide
Read the cautions before using
Methyl Thioglycolate can be useful, but watch for high irritation potential.
Plain-English read
Treat this as a practical screening step before you compare products that contain this ingredient.
- Step 1Start with the score, then check the irritation and clogging risk before judging Methyl Thioglycolate.
- Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
- Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.
Score terms in plain English
Irritation risk
highMore likely to cause dryness, stinging, peeling, or reactivity if used too aggressively.
Clogging risk
lowLess likely to feel heavy or contribute to clogged pores for most skin types.
Evidence level
moderateThere is useful support, but formula details and claim strength still matter.
What it is
Methyl thioglycolate is an organic compound (an ester of thioglycolic acid) that acts as a reducing agent. It is a clear liquid with a powerful sulfur odor and is classified as a corrosive substance in concentrated form.
How it works
It breaks the disulfide bonds in keratin, the protein that gives hair its strength and shape. This softens the hair so it can be wiped away (depilatory) or rearranged into a new shape (perms/straighteners). The effect is temporary—new hair growth will have its original structure.
Pros
Fast hair removal
Works in minutes to dissolve hair at the skin surface, making it a quick option for large areas like legs or arms.
Effective straightening
In professional settings, it can produce sleek, straight results that last for weeks, unlike temporary heat styling.
Cons and cautions
High irritation risk
Even at low concentrations, it can cause redness, stinging, and chemical burns if left on too long or used on broken skin.
Strong odor
The sulfur smell is very noticeable and can linger on skin and hair for hours, which many find unpleasant.
Best for
- People seeking professional hair removal or straightening under a trained stylist
- Those with no history of sensitive skin or allergies to sulfur compounds
Use caution if
- Anyone with sensitive skin, eczema, or active skin conditions
- Pregnant or nursing individuals (due to lack of safety data)
- People with known allergies to thioglycolates
Usage tips
Safety summary
Methyl thioglycolate is effective but carries a high risk of skin irritation and burns. It should only be used in professional settings or with extreme caution at home. Avoid contact with eyes and mucous membranes.
Research notes
Studies confirm its mechanism of breaking disulfide bonds in keratin. Safety assessments by the Cosmetic Ingredient Review (CIR) note that irritation is concentration-dependent and recommend limiting use to rinse-off products.
Common label clues
- Typical concentration
- 2–10% in professional-use products
- Regulatory status
- Approved for use in cosmetics in the EU and US, but restricted to rinse-off products and professional use. The EU CosIng database lists it as a depilatory and hair-waving agent with concentration limits.
- Common uses
- Depilatory creams, Hair straighteners, Perm solutions
- Environmental note
- Methyl thioglycolate is synthetic and may be toxic to aquatic life if disposed of improperly. Always follow local guidelines for chemical waste.
Good to know
- Methyl thioglycolate is often listed under INCI as 'Methyl Thioglycolate' and may appear in professional perm or straightening kits.
- Products containing this ingredient are typically labeled 'for professional use only' due to safety concerns.
Common questions
What is Methyl Thioglycolate in beauty products?
Methyl thioglycolate is a synthetic chemical that works by breaking the bonds in hair protein, making hair easy to remove or reshape. It has a very strong, unpleasant smell (like rotten eggs) and is typically used only in professional salon treatments because it can irritate or burn skin if left on too long. You won't find it in everyday skincare products—it's mainly in depilatory creams and hair-straightening solutions.
What does Methyl Thioglycolate do in a beauty product?
It breaks the disulfide bonds in keratin, the protein that gives hair its strength and shape. This softens the hair so it can be wiped away (depilatory) or rearranged into a new shape (perms/straighteners). The effect is temporary—new hair growth will have its original structure.
Is Methyl Thioglycolate safe for most people?
Methyl thioglycolate is effective but carries a high risk of skin irritation and burns. It should only be used in professional settings or with extreme caution at home. Avoid contact with eyes and mucous membranes.
Who should be careful with Methyl Thioglycolate?
Anyone with sensitive skin, eczema, or active skin conditions Pregnant or nursing individuals (due to lack of safety data) People with known allergies to thioglycolates
Research sources
Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.