Dandruff is a scalp problem, not a hair problem, and for most people it's less of a problem than advertisements would have you believe.

Oiliness and flakiness of the scalp are normal. The human scalp, even at its healthiest, shows a mild degree of scaling; the skin all over the body continually sloughs off bits of its dead outer layer. On the scalp, sebaceous glands add their oily secretion (sebum) to the dead skin scales, forming dandruff.

Back in the days when people washed their hair only once every week or two, this sign of the normal replenishment of scalp skin could easily drop from the hair and turn into an ugly social problem. But people now typically wash their hair almost every day, often enough to wash away the flakes before they fall. In fact, there's nothing wrong with washing your hair as often as you want. Most people, consequently, have no need for a special dandruff shampoo.

How Shampoos Work

The primary function of ordinary shampoo is to remove dirt, dead skin scales, and excess sebum from the hair. The ingredients that do the work are long molecules called surfactants. One end of these molecules is attracted to oil, the other to water. That allows them to grab sebum and whatever dirt it contains and rinse it out of your hair.

Soap, once the main cleaning ingredient in shampoos, is one type of surfactant. But soap reacts with the minerals in hard water, leaving a scummy film on hair. Such a film can be removed with an acidic rinse; that's why people rinsed their hair with lemon juice or vinegar or even beer, which is mildly acidic.

Shampoo manufacturers have since turned to surfactants less troublesome than soaps. These ingredients are often called detergents, to differentiate them from soaps. Many are derived from the fatty acids of coconuts—hence "essential fatty acids" and "coco-" ingredients.

There are dozens of these surfactants, each with its own properties. Some are much milder than the name detergent implies—they might remove dirt but little sebum, or they might not sting if they get into your eyes. Others are especially effective at penetrating and removing oil. Some clean but don't foam; others produce a rich lather. Some leave hair looking better than others do. A manufacturer usually uses several surfactants in a shampoo, one being the principal cleaning agent and the others there to modify its effect. The range of surfactants and their possible combinations provide lots of room for claims of "special" formulations.

Alkaline substances such as detergents tend to leave the hair fluffy; acidic substances such as cream rinses or lemon juice (or beer) tend to smooth it down. That's the origin of the fuss some companies make over their "pH balanced" formulas. Yet the fluffing effect of detergents used in shampoos quickly fades. And most shampoos these days are formulated to be, if not acidic, at least not very alkaline. That's typically done by adding citric acid.

Don't let yourself be intimidated into thinking you must spend a lot of money on a "hair care system" in order to have clean, "healthy" hair. As far as we can tell, relatively inexpensive shampoos contain perfectly adequate cleaning and conditioning ingredients. If you want to spend money on an expensive shampoo, do it knowing that you're indulging your psyche, not your hair.

Dandruff Shampoos

While most people don't need a medicated shampoo, some may choose to try one if frequent washing with an ordinary shampoo doesn't control the flaking. These antidandruff formulas are a special subclass of shampoo, considered by the U.S. Food and Drug Administration (FDA) to be—and therefore regulated as—drugs rather cosmetics.

The precise cause of excessive scalp flaking is unknown. Sometimes the production of oily secretions and dead skin scales speeds up until the flaking is definitely excessive. But the transition from the normal to the abnormal state can be so gradual that it is difficult to tell when one condition ends and the other begins. There is no basis for assuming, as some advertisers do, that germs are the primary cause of dandruff, and that an antiseptic shampoo is the cure. Indeed, although severe dandruff can be controlled, it cannot be cured. Spontaneous periods of improvement are common, a fact that casts doubt on all testimonials for cures with any particular product.

The FDA has judged five ingredients used in over-the-counter (OTC) dandruff shampoos to be safe and effective: coal-tar preparations (such as Denorex and Tegrin), salicylic acid (P&S, X-Seb), selenium sulfide (Selsun), zinc pyrithione (Head & Shoulders, Sebulin, Zincon), and sulfur preparations, which usually also contain salicylic acid (Sebulex, Vanseb).

Severe flaking can be a symptom of certain diseases, notably seborrheic dermatitis and psoriasis. Such conditions require diagnosis by a physician, who may prescribe special treatment beyond those OTC preparations.

There is no evidence that changes in diet or the addition of vitamins or minerals can control the development of dandruff or affect the quality of the hair in the slightest way. Nor is there any evidence that exposure of the scalp or head to sunlight either prevents or cures any type of scalp disorder.

Many men worry that dandruff might lead to baldness. Although severe dandruff and "male pattern" baldness (beginning at the temples and progressing to form a "widow's peak") may occur simultaneously, no cause-and-effect relationship between them has ever been shown. Dandruff and scalp oiliness can last for years without leading to the slightest thinning of the hair.

Most people who buy medicated shampoos fear being ostracized by a dandruff-phobic society—spurred on by advertisers for antidandruff products. These social consequences may be reason enough. But the fact is that the medical consequences of dandruff are few, if any. Some dermatologists maintain that dandruff requires treatment. But there is little evidence that scalp itching—the main symptom of dandruff other than "unsightly" white flakes—responds better to medicated shampoos than to ordinary ones.