Undoubtedly the use of dyes is not good for the hair, since they have components such as ammonia that damage it in its structure. Now, they don’t modify the scalp. There are many cases of women who have come with an oily scalp but the hair shaft is dry and damaged by dyes.
Before making a dye it is convenient to verify if one is not allergic to it, since if a severe allergic reaction occurs in the scalp due to the dye, this can cause a burn damaging the hair definitively. So before a new dye it is advisable to perform an allergic test behind the ear and see the result at 48 hours.