Allergies — how to patch test before you use

### About this concern

Indian skin tones, scalp types, and Chennai's humidity all influence how your skin reacts to a new product. Most people never patch test, then get a reaction and blame the brand. A patch test takes 24-48 hours, costs nothing, and saves a lot of trouble. This page is education only — for any real allergy or persistent rash, please see a dermatologist.

### What we know

Reactions to cosmetics and personal care come in two broad types. Irritant contact reactions happen quickly when a strong ingredient damages the skin barrier — burning, stinging, redness. Allergic contact reactions are immune-mediated, can show up 12-72 hours after contact, and tend to recur with the same ingredient. Common Indian triggers we see: hair dye (PPD), fragrance, certain preservatives (parabens, formaldehyde-releasers like DMDM hydantoin), sulphates in shampoos (SLS/SLES) on sensitive scalps, nut-derived oils in haircare and skincare (almond, walnut, hazelnut), nickel in jewellery, henna mixed with PPD, and certain essential oils.

### What to watch for

• Redness, itching, burning, stinging, small bumps, or peeling at the application site.
• Watery eyes or sneezing from fragrance.
• Scalp itch, dandruff-like flakes, or hair fall after a new shampoo or oil.
• Swelling of lips or eyes after a lip or eye product — stop immediately and seek care.
• Hives anywhere on the body shortly after a product — stop and seek care.

### What you can do safely

How to do a 24-hour patch test at home:

1. Pick a clean, hair-free spot on the inner forearm, near the elbow crease, or behind the ear.
2. Apply a coin-sized amount of the product. For rinse-off products like shampoos, dilute slightly with water.
3. Leave for as long as you would normally use it. For leave-on products (cream, serum, oil), leave for 24 hours, reapplying once.
4. Do not wash the area for 24 hours.
5. Check at 24 hours and again at 48 hours.
6. If you see redness, itching, bumps, burning — do not use the product. Wash gently with mild soap.

Ingredient classes to watch for if you have known sensitivities:

• Fragrance / parfum — even in "unscented" products sometimes.
• Parabens — common preservative, generally safe but can sensitise some people.
• Formaldehyde releasers — DMDM hydantoin, imidazolidinyl urea, quaternium-15.
• Sulphates — SLS, SLES — can dry out sensitive scalps and skin.
• Nut-derived oils — sweet almond, walnut, hazelnut — risky if you have a nut allergy.
• PPD (paraphenylenediamine) — in most hair dyes and some "black henna".
• Essential oils — tea tree, lavender, citrus oils can sensitise.

General safety habits: introduce one new product at a time, wait a week before adding another, and keep a small note of any reaction so you can avoid that ingredient again.

### When to see a doctor

Please consult a dermatologist if a rash does not settle in 3-5 days, if it spreads, weeps, or crusts, if you have repeated reactions to many products, if your scalp itch becomes painful, or if your hair fall is sudden and dramatic. Seek urgent care for any swelling of lips, tongue, eyes, breathing difficulty, or full-body hives. If you are pregnant, lactating, on prescription skin medication (isotretinoin, steroids), or treating a chronic skin condition like eczema or psoriasis, ask your doctor before trying new products.

### What we do NOT recommend over the counter

We do not recommend strong steroid creams, depigmenting creams, or fairness creams sold without prescription — these are widely misused in India and damage skin. We do not recommend home remedies for an active allergic reaction. Please do not use any new product on your face or scalp before completing a patch test on your forearm.