As the mother of two children who have had their fair share of lice scares, I am acutely aware - and suspicious - of head scratching of any sort, including my own.
But most of the time, an itch on the noggin is most likely related to dandruff, a common inflammatory scalp condition, says Lynn McKinley-Grant, an associate professor of dermatology at the Georgetown University School of Medicine. "Everybody seems to have at least a little dandruff," she says, noting that other symptoms include flaking, redness and occasional tenderness. The condition, which affects nearly half of the post-puberty population, crosses gender, racial, ethnic and age lines; a recent survey found that people in the United States shell out nearly $300 million a year on shampoos and other products to control it.
Still, doctors know relatively little about how dandruff works or who will be most prone to it. What we do know is that oil on the scalp plays a role, says Antonella Tosti, a professor of dermatology at the University of Miami who specializes in hair and nail health. "Everybody needs sebum, or oil - it's an important part of the health of the skin and scalp - but sometimes it can lead to inflammation and the hyperproliferation of skin cells." Normally, she explains, it takes skin cells on the scalp around 28 days to mature, die and shed, but in people with dandruff they never fully mature, flaking off in huge clusters in just seven to 10 days.
Recent research has documented yet another contributing factor: a common fungus called Malassezia. "This yeast is a normal colonizer of the scalp - everybody has it - but in some people and under some conditions, it hyperproliferates," which can trigger inflammation and the excessive shedding of skin cells, Tosti says. "We just don't know why that's true for some people and not others."
Certain environmental triggers can make dandruff worse, particularly at this time of year. "It usually exacerbates in winter and in [a] dry climate," Tosti says, adding that dietary factors such as alcohol intake and an overly greasy diet may worsen the condition, as may psychological stress. Experts also report that the severe form of dandruff, seborrheic dermatitis, is more frequent in people with such neurological diseases as Parkinson's, in stroke victims and in those with HIV. "But we don't know why," she says.
Although dandruff is a chronic, recurrent condition for many, it is eminently treatable. The key, say all of the experts I spoke with, is shampooing often and, more important, shampooing properly.
"It's important to distinguish between shampooing the scalp and shampooing the hair," Tosti says. Indeed, Washington dermatologist Ella Toombs recommends applying a dandruff shampoo while your scalp is dry, massaging it in well and letting it sit for at least 10 minutes; only then should you add water to make a lather, running an old brush along the scalp in a circular motion to remove flakes and to help the shampoo's active ingredients reach the skin, and then rinse. Afterward, McKinley-Grant suggests, use a high-quality regular shampoo to make hair feel nicer. She also suggests switching your dandruff product every now and again to maintain its effectiveness.
As for choosing a treatment: Drugstore shelves are full of shampoos containing zinc, coal tar and salicylic acid, which each work for different symptoms. For example, the last of these is best for scale, says McKinley-Grant. She notes that it can take some trial-and-error to find the product that is best for you.
If your over-the-counter shampoo isn't making a difference, McKinley-Grant recommends seeing a dermatologist for a more targeted treatment, such as a topical steroid that counters inflammation. It's also important to rule out a fungus, which may require a prescription drug. A study published this year identified an enzyme in one particular Malassezia species that is essential for its growth; it also found that topical sulfonamide antibiotics were more effective in preventing said growth than ketoconazole, which is found in many anti-dandruff treatments.
For those who aren't too worried about a few flakes on their dark suits or sweaters, there's this: The condition may play a role in premature hair loss, Tosti says. "If this person who has dandruff also has a genetic predisposition to develop baldness, that's where you really have to control it well, because the inflammation is going to induce and also speed up to the acceleration of hair loss, for both men and women," she explains. But for most people, dandruff is really a cosmetic concern: "It's an annoyance and it's not all that attractive at times," Toombs says, "but it doesn't harm anybody."