Hair dyes can damage the hair as they alter the hair structure in order to fix the colour pigments in the middle layer (cortex), which is where the natural pigments that provide the natural colour of the hair are located.
This process causes the porosity of the hair to increase. Their regular use is not related to any type of alopecia, as they do not act on the hair follicle, but excessive use can weaken the hair shaft and lead to more dehydrated and dry hair. Dyes can also cause allergies and the main symptoms are itching, irritation and burning of the scalp, or swelling of the eyelids or face.