Unfortunately, establishing that you’re sensitive to PPD AND PTD generally involves experiencing a reaction to it - there’s no way to test other than applying dye to the skin. But dyeing the hair and hoping for the best is distinctly inadvisable, which is where patch tests (or ‘skin tests’) come in. The purpose is to alert you about an allergy, therefore it is also called allergy alert test.
Patch tests allow a small, controlled amount of dye to be tested and the skin’s reaction to be monitored, and should always be carried out before using a permanent or semi-permanent dye, even if it’s one that’s been used before. This is partly because the formulation may have changed, but also because when allergies develop, it’s frequently after repeated exposure. Using a dye safely for years is no guarantee that it will remain safe to do so.
The patch test involves a small amount of dye being dabbed on the skin, usually in the crook of the elbow or behind the ear, and leaving it to dry. This can be done at home, a salon or an allergy clinic. If the test causes redness, irritation or itching, then the dye shouldn’t be used. If there’s no reaction, it’s safe to go ahead. However, it’s important to carry out the test 48 hours before the salon appointment or before you intend to dye at home. It’s tempting to skip this step because it’s not always convenient to pay two visits to the salon, and impatience can easily get the better of the home user, but it’s better to err on the side of caution because the reaction may be significantly delayed.
If you’re carrying out a patch test at home, it’s important to remember that it’s PPD AND PTD vital that the mixed dye (tint mixed with developer) is tested on the skin, not just one element or the other.
It’s also advisable to patch test treatments such as highlights, because even though foils are used, product could leak onto the scalp.
This is the new name for the skin test agreed by hair dye industry. It would be great introduce it.
It is not clear what form of PPD, but mixing of tint and developer is relevant to mimic what happens during hair dyeing.