Colouring hair can, in some people, cause an allergic reaction resulting from chemicals in hair dye absorbing into the skin. Individuals who have this allergy often complain of a dry, itchy scalp.
Hair dyes contain several elements that might provoke an allergic reaction, most typically para-phenylenediamine (PPD).
PPD is the most common culprit of an itchy scalp after a colour treatment. It is found in approximately two-thirds of all hair colouring products. Other chemicals that can provoke an allergic reaction are hydrogen peroxide and ammonia.
Symptoms of an allergy to PPD can occur right after a hair treatment, several hours or even days later, or after several treatments. Those who have strong allergic reactions can also experience redness, a burning feeling, swelling of the eyelids, asthmatic symptoms, vomiting and, in severe cases, anaphylactic shock.
To prevent problems with hair colouring treatments (both at a salon and at home), look for products that are natural and read the labels carefully. In addition, perform a test strain to see how your scalp will react.
Try using an anti-itch shampoo, such as Head n' Shoulders, for relief. If the itchiness is mild, soothe your head by rubbing your fingertips along the scalp (do not use your nails). If your reaction is moderate to severe, seek medical attention.