Before using any permanent hair colour, you should do a patch test to check for an allergic reaction. Apply a small amount of the mixed colour (following the product's instructions) to a small area of skin, usually behind the ear or on the inner elbow, and wait 48 hours. If you notice any redness, itching, or swelling, do not use the product. This is a safety step that the manufacturer explicitly recommends.
In addition to the patch test, do a strand test to see how the colour will look on your hair. This is especially important if your hair is very dark, previously coloured, bleached, or uneven. The strand test will show you the final tone, coverage, and how long you need to leave the colour on. It also helps you avoid a full-head surprise.
Be extra cautious if your scalp is sensitive or if your hair has been recently bleached, permed, or heavily heat-styled. These conditions can make the hair more porous and the colour may take unevenly or cause irritation. If you have any skin condition, are pregnant, breastfeeding, or are taking medication that affects your skin, consult a specialist before use. Follow the instructions included in the package for mixing, application time, and rinsing – do not leave the colour on longer than recommended, as this can damage the hair.