There is a great deal of confusion regarding skin tests for hair colour.
I will attempt to clarify the issue here.
Why do we need to do skin (patch) allergy tests?
Skin tests are required for the permanent colouring of hair. You should check the manufacturer’s instruction to see if a skin test is required for your brand of true (where there is no mixing) semi-permanent colours, temporary colours or bleach. The reason for this is that permanent (and some other) hair colouring products contain an ingredient called PPD or paraphenylenediamine sometimes called p-phenylenediamine. It is there to assist a lasting colour result. The problem is that a small number of people (around 0.1% of the population) have the potential to develop an allergic reaction to PPD and the reaction can be very intense.
In order to predict if you have the potential to react to PPD a tiny amount of the product to be used should be placed on the skin and left uncovered for 48 hours. This time is required because it can take up to 48 hours for a reaction to occur.
If a reaction (itching, redness or swelling) around the test area does occur then the colouring procedure cannot be carried out as the risk of allergic reaction is too great and you the customer should seek medical advice about the colouring of your hair.
Do allergic reactions happen often?
No, allergic reactions are rare, considering that Millions of people all over the world use hair colourants without experiencing any unwanted effects. In the UK alone, around 100 million hair colourant applications are carried out every year in homes and salons. Hair colourants are one of the most thoroughly studied consumer products on the market and their safety is supported by a wealth of scientific research. In fact, allergic reaction to hair colourants is much rarer than an allergic reaction to food.
Anyone who has the potential to react to PPD may not react the first time they encounter it. However, the early exposures will prime their immune system which may then over-react when they encounter PPD again. Essentially, the immune system identifies PPD as a foreign body and remembers it. When that element is encountered again, it is the over-reaction of the immune system rather than the ingredient itself that causes the damage.
Not everyone has that potential to develop an allergy. Those who have the potential will, sooner or later, produce an allergic reaction if they continue to be exposed to PPD.
Some products claim to be PPD free but PPD is required in all permanent hair colour products, some colourants use an alternative, PTD (para-toluenediamine). PTD can also lead to allergic reactions in those sensitive to either PTD or PPD. For this reason, all hair colourant products that contain PPD, PTD or any other chemically similar dye must include the warning ‘Contains phenylenediamines’ on the packaging.
Can you the customer sign a waiver in order to avoid performing a prescribed skin test before a colour service?
No, you cannot, regardless of what you sign, the hairdresser would still be negligent. The issue is one of insurance. All salon insurance policies state that Manufacturer’s instructions must be followed. Failure to follow Manufacturer’s instructions will void the insurance and the salon business will become directly liable.
Although a skin allergy test must be completed at least 48 hours before colouring the hair, it remains valid for around 6 months. This means that if you have your hair coloured regularly you will in effect be having a skin test done every time you have your hair tinted.