Seborrheic dermatitis; hair dyeing in elderly; age-related hair growth patterns

Q. Why can't I find a shampoo that combines salicylic acid with tar for my seborrheic dermatitis patients?

A. This is an interesting question with a simple answer and a long explanation. The simple answer is that such a shampoo is illegal in the United States.

The long explanation is that dandruff shampoos are considered over-the-counter drugs and as such fall under specific governmental regulations. Dandruff shampoos by law cannot contain more than one active ingredient selected from a list of approved agents put forth in a monograph. While it would be worthwhile to have a dandruff shampoo that combined salicylic acid as an effective keratolytic with tar as an effective anti-inflammatory, the government feels that this combination should not be marketed. For this reason, it is necessary for the dermatologist to recommend the rotation of dandruff shampoos to achieve optimal control of seborrheic dermatitis.

A. Even though mild to moderate dandruff does not cause hair loss, the scratching associated with the scalp pruritus can definitely predispose to hair loss.

It is possible to remove all of the cuticular scale from a hair shaft with only 90 minutes of continuous scratching by the fingernails. This loss of cuticular scale leaves the hair shaft weakened and permanently cosmetically damaged. It is for this reason that treating scalp itch is important for cosmetically attractive hair. Indeed, patients may notice improved hair growth following treatment for seborrheic dermatitis.

Q. Why is it difficult to dye gray hair?

A. Gray hair that possesses decreased pigment is less likely to dye to as deep a color as youthful hair that contains melanin pigment.

This is due to the fact that the permanent hair dye interacts with the melanin to produce the final hair color. Hair that is deficient in melanin will still dye, but not to as deep a color, and the hair coloring will not last as long. For this reason, it may be advisable to consider selecting a lighter hair color as the hair grays. Lighter hair colors also will not fade as frequently, allowing the period between hair dyeing to be extended.

Q. How do changing hair growth patterns with age affect dyeing and permanent waving in the elderly?

A. It is a well-known fact that hair growth slows down with age. This means that cosmetically damaged hair will be present longer on mature individuals.

Also, the diameter of the hair shaft decreases with advancing age. This predisposes the thinner hair shafts to chemical damage from chemical processing. For this reason, all chemicals used on mature hair should be weaker than those used on youthful hair. For example, the perming solution should be weak and left in contact with the hair for as short a period as possible. Hair perming should always be performed prior to hair dyeing and the two procedures separated by at least two weeks. Slower hair growth and thinner hair shafts mean special care must be taken not to permanently damage the nonliving hairs through aggressive chemical contact.

Zoe Diana Draelos, M.D., is a clinical associate professor of dermatology, Wake Forest University School of Medicine, Winston-Salem, N.C., and primary investigator, Dermatology Consulting Services, High Point, N.C. Questions may be submitted via e-mail to

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