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19. Hair Straightening and Hair Dyes: Facts and Controversies
Keywords
Hair dyesHair relaxersHair straighteningPermanent wavingBrazilian keratin treatmentBleaching agentsIntroduction
Hair dyes and hair relaxers are hair care products commonly used to change hair color and shape, respectively. Very popular among patients, these products may be self-applied as a home care treatment or by a professional hair stylist at the hair salon. These products can cause adverse reactions, particularly after improper use. In this chapter, we discuss hair straightening products and hair dyes, their mode of action, recommendations, and possible side effects.
Straightening and Permanent Waving [1–11]
Hair straighteners are also called chemical relaxers, because the straightening effect on the hair shaft is permanent. The high pH (9.0–14.0) of the emulsion swells the hair, thus opening cuticle scales, which allows the alkaline agent to penetrate into the hair fibers up to the endocuticle. Once in contact with the cortex, the straightening product reacts with keratin, breaking and rearranging the disulfide bridges, and making the spiral keratin molecule soft and stretchable.
The most popular relaxers for African-textured hair are hydroxide relaxers. They can be separated into lye (which contains sodium hydroxide) and no-lye (which contains calcium hydroxide or guanidine hydroxide) agents. The lye-based relaxers, which have a higher pH, have a fast onset of action (might straighten the hair in only 20 minutes) and are less damaging for the hair shaft but can cause scalp irritation. They must be applied by cosmetic professionals. The no-lye relaxers are less irritating to the scalp but can leave mineral deposits behind, causing dry, brittle hair. After the original application, the relaxer is reapplied every 6–8 weeks to the hair root to act on the recently grown virgin hair.
Lye and no-lye relaxers react with keratin cystine groups, producing lanthionyl residues, a stable thioesther crosslink. After cleavage of the disulfide bonds, the hair is mechanically straightened using a comb to restructure the position of disulfide bonds between new polypeptide keratins.
Relaxers for Caucasian and curly hair contain thioglycolic acid and its derivatives, such as 7.5–11% ammonium thioglycolate and bisulfite, pH between 9–10. They are milder than the hydroxide relaxers and are not the first choice for African hair. The same chemicals are also utilized in permanent waving. The desired hair shape is obtained by breaking the cystine disulfide bonds between the keratin filaments and then forming cysteine. A large number of bonds are, however, lost with the procedure, resulting in permanent reduction of the hair strength and protein loss. For straightening, the perming lotion is first applied to the hair that is then treated with hot iron; for perming, it is applied to the hair wrapped around rollers of different size depending on desired result. When the keratin linkages are broken, a neutralizing lotion containing an oxidizing agent such as hydrogen peroxide, is applied in order to remake new disulfide bonds in the desired shape.
The process is delicate, because when the disulfide bonds are broken, the hair shaft is vulnerable and can be easily be broken. Factors that most commonly produce hair breakage include sudden changes in the temperature and mechanical trauma. Hair damage can also be caused by overperming, poor neutralization, or formation of new incomplete bonds due to shampooing the night or a few days after the procedure. Hair breakage occurs close to the scalp and usually happens a few days after the procedure. Chemical relaxers, even if properly applied, damage the hair fiber due to protein loss and removal of the superficial lipid film of 18-metil eicosanoic acid (18-MEA). Irritant and allergic contact dermatitis are other possible complications.
Hair straightening/perming with chemical relaxers usually needs to be repeated every 12–24 weeks. Only the new growing hair should be processed, as repeated treatments lead to hair breakage, which usually occurs at the junction of the new growing and previously treated hair.
Tips to avoid hair damage
Do not shampoo for at least 3 days after permanent relaxing or permanent waving. |
Bleaching is very damaging to the hair shaft and the hair becomes thinner after bleaching. |
Bleached hair is very susceptible to sun damage. Never bleach your hair just before a summer vacation! |
Never relax bleached hair. Bleached hair is sensitive to relaxing and may break. |
Never mix two types of hair relaxers. Hair relaxed with thioglycolate will break if treated with guanidine. |
Before relaxing, apply the product to a hair strand and wait to see if the hair resists the stress. |
Be sure to treat only the hair root if your hair has already been relaxed or permanently waved. |
Dye hair within your natural color or darker; this will minimize hair damage. |
Patients allergic to PPD should be patch-tested with para-toluenediamine sulfate as this can be a safe alternative. |
Always permanently wave or straighten hair first, waiting at least 2 weeks before undergoing a hair dye procedure. |
After bleaching, use a deep conditioner. |
If your natural color is dark, do not go to pale blonde or the hair will get too damaged. |
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