Hair can be straightened using a keratin treatment, a hair relaxing treatment, Japanese thermal straightening, alkaline straightening or using a blow dryer. If a chemical treatment is used, however, there may be health risks involved.
Some people prefer to straighten their hair chemically to avoid the heat damage from flat irons and blow dryers. However, chemical treatments, such as Brazilian blowouts, and other keratin treatments often contain formaldehyde that is released into the air or absorbed.
Other hair straightening techniques, such as Japanese straightening, are more permanent and must involve the breaking of disulfide bonds between hairs. This can be very damaging to the hair structure. Thioglycolates and lye-based alkalines are often used and can cause allergic reactions, scalp and respiratory irritation and chemical burns.