Hair dye is generally considered safe to use during pregnancy. The NHS and ACOG note that only a small amount of the chemicals in permanent and semi-permanent dyes is absorbed through the skin, and that amount is too low to be expected to harm the baby. If you'd like extra peace of mind, you can wait until the second trimester, work in a well-ventilated room, or choose highlights, which keep the dye off the scalp.
Hair dye covers permanent, semi-permanent, and temporary colors, plus highlights and bleach. Most contain chemicals like ammonia and peroxide, and some permanent dyes contain PPD (para-phenylenediamine). The NHS notes that very little dye is absorbed through the scalp, which is a large part of why it is considered low risk. Highlights and balayage touch even less skin, since color is applied to the hair strands rather than the roots.
The NHS states that the chemicals in hair dye are not highly toxic and that most research, though limited, suggests it is safe to color your hair during pregnancy. ACOG and the American Academy of Dermatology broadly agree that occasional use is unlikely to be harmful. The reason experts stop short of a firm all-clear is that studies are small and no large trials confirm long-term safety, so guidance leans toward moderation rather than a green light.
Some clinicians suggest waiting until after the first trimester, when the baby's major development is complete, though the NHS notes there is no strong evidence this is necessary. To reduce exposure, color in a ventilated room, wear gloves, leave dye on for the minimum time, and rinse the scalp well. Highlights, balayage, or plant-based options like pure henna limit scalp contact further. Do a patch test first, since pregnancy can change how your skin reacts.