Chemical depilatory

A chemical depilatory is a cosmetic^[1] preparation used to remove hair from the skin on the body. Currently, common active ingredients are calcium thioglycolate or potassium thioglycolate, which breaks down the disulfide bonds in keratin and weakens the hair so that it is easily scraped off where it emerges from the hair follicle.

This break down reaction is affected by the calcium hydroxide or the potassium hydroxide (both alkali). The resulting combinations of calcium hydroxide or potassium hydroxide and thioglycolic acid are calcium thioglycolate(CaTG) or potassium thioglycolate (KTG), respectively. The calcium hydroxide or potassium hydroxide are present in excess to enable the thioglycolic acid to react with the cystine present joining chains in hair protein. The reaction is:

2 HSCH₂CO₂H (thioglycolic acid) + R-S-S-R (cystine) → HO₂CCH₂-S-S-CH₂CO₂H (dithiodiglycolic acid) + 2 RSH (cysteine)

As the epidermis is also rich in keratin, the skin may become irritated and sensitive if the preparation is left on for too long. Chemical depilatories are used primarily for the arms and legs. They should not be used on the face unless specifically listed for that purpose on the product's label.

Chemical depilatories are available in gel, cream, lotion, aerosol, roll-on, and powder forms. Common brands include Nair, Magic Shave and Veet.

Advantages

• Inexpensive
• Fast
• A pain-free hair removal method
• Easy to do, no experience or professional assistance required
• Can be done at home
• Available over-the-counter

Disadvantages

• Effect lasts a short time. Regrowth begins to appear generally within 2-5 days
• Dark-haired users may be left with a visible "shadow" of dark hair under skin
• Chemical depilatory creams are generally foul in odor and messy to use
• Can cause skin irritation

References

1. "Skin care cosmetic preparation".