Bontress pro hair serum ingredients is generally well-tolerated, but like any cosmetic product, some individuals might experience mild side effects. These can include scalp irritation, itching, redness, or a burning sensation. In rare cases, allergic reactions like rash or hives might occur. If you experience any persistent or severe side effects, discontinue use and consult a dermatologist. It's always recommended to perform a patch test before the first application to check for any sensitivity.