Resorcinol
Also known as1,3-benzenediol, m-dihydroxybenzene, CAS 108-46-3
FunctionDye coupler — common allergen
What it is — Resorcinol (1,3-benzenediol, CAS 108-46-3) is a small synthetic aromatic compound. In hair colour it is a coupler: it does not colour hair by itself but reacts with a primary intermediate such as p-phenylenediamine (PPD) or p-toluenediamine (PTD) inside the hair shaft to build the final brown, ash and neutral tones. It is also used in some acne and peel products at low levels, and industrially in resins and rubber.
Where you meet it — Permanent (oxidative) hair dyes, colour-depositing hair dye shampoos and colour lotions. In a hair dye shampoo it is normally the second or third colour-forming ingredient after the primary dye, at a fraction of a percent.
What the regulators say — The EU Scientific Committee on Consumer Safety (SCCS) reviewed resorcinol in 2010 and again in 2021. It is listed in Annex III of the EU Cosmetics Regulation: allowed as an oxidative hair colourant up to 1.25% applied to the hair (after mixing), and up to 0.5% in hair lotions and shampoos. Products must carry the standard hair-dye warnings, including "can cause an allergic reaction" and the 48-hour skin test. The US Cosmetic Ingredient Review (CIR) Expert Panel has likewise concluded it is safe within current practices of use.
Why the concern — Resorcinol is a recognised skin irritant and a documented contact sensitiser in hair-dye users, although PPD and PTD cause far more dye allergies. Animal studies also show it can interfere with thyroid hormone synthesis at high oral doses, which is why the EU examined it under its endocrine-disruptor programme and why programmes such as EWG VERIFIED exclude it. The SCCS concluded that dermal absorption from hair dye is too low for a thyroid effect at permitted levels, but DHALIORA grades on hazard as well as exposure, so it stays high on our list.
Practical rules — Do the 48-hour patch test every time, even with a product you have used before. Wear the gloves. Keep the product off broken or irritated scalp, rinse thoroughly, and stop if you get burning or swelling. Anyone with a known PPD, PTD or hair-dye allergy should treat resorcinol-containing colour with the same caution, since the products are almost always combinations.
How DHALIORA handles it — We disclose it on every product that contains it (you will see those products listed below) rather than hiding it behind a "free-from" claim. This is general ingredient information, not medical advice.
Found in these DHALIORA products
Found in 2 DHALIORA products
