Patch testing is the simplest way to avoid a bad reaction. It takes two days and needs nothing but a clean cotton swab.

How to do it

1. Clean a small area of skin, such as the inner arm or behind the ear. 2. Apply a small amount of the product, about the size of a pea. 3. Leave it uncovered and wait for 24 to 48 hours. 4. Check the area for redness, itching, swelling or a rash.

What to do if you react

Wash the area with clean water and do not use the product again. If the reaction is strong, or it spreads, see a doctor.

Apply this to every product

This includes Glow Cream, oils, shampoos, soaps and face packs. Patch testing matters most for children, people with sensitive skin and anyone trying a new ingredient for the first time.