Why is a patch test required before every use, and how do I do it correctly?

Because this product uses an oxidative system with hydrogen peroxide developer, sensitisation can develop at any time — even if you have used the same or similar brow tints before without issues. The patch test is not optional: mix a pea-sized amount of tinting cream with the developer in the ratio indicated in the leaflet, apply a small dab behind the ear or on the inner forearm, and leave it uncovered for 48 hours. Watch for redness, itching, swelling, burning, or any skin change at the test site. If any reaction occurs, rinse immediately and do not use the product on your brows. Also skip the treatment if the skin around your brows is irritated, sunburned, broken, or if you have recently used strong actives (retinoids, acids, peels) in that area. If you have ever reacted to hair colourants, black henna tattoos, or PPD-containing products, consult a dermatologist or licensed beauty professional before proceeding.