I understand that the active ingredient in hair removal cremes is calcium hydroxide. Are there others? This is an alkali. But does it just dissolve the hair? What are the by-products? How does it work?

Available in gel, cream, lotion, aerosol, and roll-on forms, depilatories contain a highly alkaline chemical--usually calcium thioglycolate, calcium hydroxide, or sodium hydroxide--that dissolves the protein structure of the hair, causing it to separate easily from the skin surface.

It's very important to carefully follow the use directions for depilatories and to do a preliminary skin test both for allergic reaction and sensitivity. Hair and skin are similar in composition, so chemicals that destroy the hair can also cause serious skin irritations--possibly even chemical burns--if left on too long.

The concentration of active ingredient is generally kept as weak as possible to avoid skin irritation, yet strong enough to work in a reasonable amount of time. Contact with the skin is kept to somewhere between 4 and 15 minutes, depending on how fine or coarse the hair is.

Consumers should be sure to read the product label and select the formulation appropriate for the intended use, because skin sensitivity varies on different parts of the body. Some depilatories are for use only on the legs, for example, while others are safe for more sensitive areas, such as the bikini line, underarms and face.

Depilatories should not be used for the eyebrows or other areas around the eyes, or on inflamed or broken skin. To minimize the chance of skin irritation, they should not be applied more often than recommended on the product label.

Although cosmetics are not subject to premarket approval, regulators can take action against products that are found to cause harm. Several depilatories, most notably Epil-Stop, have been forced to do recalls due to shoddy manufacturing which led to very high concentrations of caustics.

A depilatory can cause second- or third-degree burns, and possibly scarring, if its formula is too strong or if an inactive ingredient in the product heightens its effect.

That's why it's very important to use these products according to instructions and with great caution. They should be removed immediately if you feel any sort of burning occurring in the treated area.