One gets scalp burn from a chemical relaxer due to improper application and/or irritation to already sensitive skin. Because relaxers often contain harsh chemicals, it is important to know one's skin type prior to application of the product.
There are a number of different brands of chemical relaxers, all of which boast the most effective form of hair straightening. While each brand may vary slightly in their delivery of the straightening process, they all share the common premise that vigilant timing and consistent application are imperative safety precautions.
One common way to cause scalp burn is by applying the relaxer directly on the scalp instead of on the hair as the instructions direct. Another common mistake is applying the product on hair that has recently been washed or near a scalp that has recently been scratched. Washing and scratching leave small incisions in the scalp which make it susceptible to chemical burns. Finally, the most common way one gets scalp burn from chemical relaxers is by leaving the product on the hair longer than the recommended time period. The directions give specific instructions on how long the chemical should be left on the varying types of hair (coarse, normal, and mild) and if the instructions are not expressly followed, the user is susceptible to scalp burn.