A strand of hair is a complex nonliving structure, containing about 95 percent protein (called keratin, also the building block of fingernails), plus some pigment (melanin) and fats. The thin outer cells of a strand are called the cuticle—a layer of tiny flaps, like scales. Inside the strand are tinier strands called fibrils. The geometry of hair determines its appearance: Thick round strands lie flat and straight, while flatter hair shafts tend to curl. As hairdressers know, most people want the kind of hair they haven’t got.
You can be healthy without a hair on your head, but many of us are distressed by hair loss, or by hair in poor condition. Nearly anything you do to hair, including combing, damages it to some degree. No wonder there’s a multibillion-dollar industry catering to consumers who seek luxuriant locks. The problem is there’s little solid research on many of the hair treatments and products marketed, often by celebrities—and much misinformation on the Internet.
We set the record straight here with answers to some common questions about hair, from how to make the most of what you have to how your hair might (or might not) reflect your health.
Q: Should I brush my hair 100 strokes a day, like grandma said?
A: No. Before the advent of hot running water and comfortable indoor temperatures in winter, brushing hair vigorously helped keep it clean; now we shampoo. Brushing and combing too vigorously tends to damage the cuticle, breaking off some of the microscopic scales. It’s worse when hair is wet, because the fibers are swollen with water and more susceptible to damage from the brush. Avoid brushing wet hair, especially if your hair is in fragile condition; use a wide-toothed comb instead. Or just use your fingers to arrange your hair and let it dry naturally.
Q: What kind of shampoo is best?
A: All shampoos contain detergents along with a long list of other ingredients, including fragrances in most. For people who have a moderate amount of scalp sebum (the oily substance produced by the sebaceous glands in skin) and don’t have chemically treated hair, any regular shampoo is suitable. Shampoos for dry hair often have some conditioning ingredient and mild detergents, making them also better for chemically treated or physically damaged hair. For those who produce a lot of sebum, there are shampoos for oily hair. These contain detergents that have good cleaning qualities and no conditioners.
There are also shampoos labeled specifically for use on chemically treated hair and medicated shampoos for various scalp conditions, such as seborrheic dermatitis, a cause of dandruff. But since the point of shampoo is to get your hair clean, buy what works for you, keeping in mind that, according to the American Academy of Dermatology, “Regardless of cost, many shampoo and conditioner brands provide the same benefits.”
Q: What do conditioners do?
A: Conditioners contain proteins and other ingredients that coat hair cuticles and temporarily seal split ends; some can penetrate the hair strands through defects in their protective cuticle scales. This can make hair smoother, thicker, shinier, less frizzy, and easier to comb and detangle. Conditioners can also minimize breakage. All of this is temporary, however, because any ingredients that penetrate the hair shaft diffuse out with subsequent washing. Still, conditioners can be especially useful for hair that’s been damaged, whether from coloring, straightening, curling, excessive brushing, or drying.
Q: Are there benefits of using “deep” conditioners or hot oil treatments?
A: Deep conditioners (which are usually left on for 20 minutes or so) and leave-in conditioners are more viscous and often contain emollients or a higher concentration of ingredients. They’re meant to be better than regular conditioners in penetrating the hair shaft and staying on or in it between washings.
Any oil can also act as a conditioner, and applying heat may help the oil better penetrate the hair shaft, because the small breaks in the hair shaft will enlarge when heated. These treatments are typically used for very dry hair that’s been repeatedly color treated or otherwise damaged. But they can make straight or fine hair look limp and oily.
Q: Does blow drying damage hair?
A: Yes, to varying degrees, depending on how it’s done. The dryer removes the moisture from the hair strand. As you’ve probably noticed, humidity can quickly put it back, altering the style. To reduce damage, wait until your hair is mostly dry, use a low heat setting, hold the dryer six inches away from the hair, and move the dryer continuously.
Flat irons and curling irons can be even more damaging to hair. Avoid or use them only on occasion—and only on dry hair. You can also apply a heat protectant before blow drying or flat ironing. These products contain ingredients such as silicones, which provide a protective coating and help prevent water loss.
Q: Does sunlight damage hair?
A: Sunlight makes hair brittle, decreases its luster, and roughens the texture. It also affects the color, turning brown hair reddish and blonde hair lighter. Dyed or bleached hair will change color even faster.
Hair products with sunscreen, including some shampoos, may help a little. Protecting your hair is one more reason to wear a hat with a broad brim in the sun. Pool chemicals and sea salt can also damage hair. For protection when swimming, wear a cap or apply a leave-in conditioner or oil (such as olive or coconut oil) before taking the plunge.
Q: Is hair dye bad for hair?
A: Like any other process (chemical straightening or relaxing, for example), hair coloring damages hair. Nevertheless, millions of people are willing to settle for more brittle hair if it’s the right color. Permanent dying is actually two processes: You bleach out the natural pigment, usually with hydrogen peroxide, and simultaneously add the new color. The dye penetrates the hair shaft.
Hair dye is not known to cause hair loss, but a chemical still found in some permanent dyes, para-phenylenediamine (PPD), has sometimes been linked with severe allergic reactions. People with such allergies may also need to avoid semi- or demi-permanent dyes, since they could develop an allergy to a chemical usually used in those formulas, para-toluenediamine sulfate (PTDS), which goes by other names, as listed at PubChem. PTDS is used in some permanent dyes, too.
Q: Are salon hair-straightening and smoothing treatments safe?
A: For some curly- or frizzy-haired people, the allure of straight, flat hair (from such processes as the Brazilian Blowout), even on humid days, seems worth almost any risk. But the Occupational Safety and Health Administration (OSHA) has found that some of the products contain formaldehyde or ingredients that release formaldehyde at unsafe levels during use. Besides being a known carcinogen, formaldehyde can cause eye, nose, and lung irritation; nausea; rashes; and other symptoms in people exposed to it, with the risks far greatest to salon workers.
Some manufacturers may list formaldehyde by other names (such as methylene glycol, formalin, methylene oxide, paraform, formic aldehyde, methanal, oxomethane, oxymethylene, or CAS Number 50-00-0), or they may claim the product is “formaldehyde-free” when it contains chemicals (such as timonacic acid, also called thiazolidinecarboxylic acid) that can release formaldehyde.
If you still want the treatment, ask to see the product label and Material Safety Data Sheet (MSDS) to check for these chemicals, though, as OSHA found, the hazard information on MSDSs was not always complete. Note also that even if products are truly formaldehyde-free, they may still contain other hazardous chemicals. No matter what product is used, make sure the area is properly ventilated with a local exhaust system that captures and removes the fumes, as shown in this video.
Q: Can pulling hair into a tight hairstyle or wearing a tight hat cause hair loss?
A: Possibly. A type of hair loss called traction alopecia can occur when hair is pulled into a ponytail, braids, weaves, or other tight hairstyles—especially if this is done over a long period of time or if the hair has been chemically treated.
If the hair loss has not been occurring for too long, the hair will grow back if you loosen or alter the hairstyle. Otherwise, over the long term, the hair loss can become permanent. Though wearing a hat is sometimes blamed for hair loss, the hat would have to be extremely tight for this to occur—too tight to tolerate for long.
Q: What causes patchy hair loss?
A: Alopecia areata (“area baldness”) is an autoimmune disorder with both a genetic and an environmental component. Affecting an estimated 6.8 million people in the U.S., male and female, it causes the immune system to attack hair follicles (but not shut them down), resulting most commonly in coin-sized bald patches. Sometimes there is complete hair loss (as experienced by Madison Jordan, who appeared in the latest season of the popular TV show “So You Think You Can Dance”).
If you have alopecia areata, a dermatologist can inject corticosteroids into the scalp or prescribe other treatments, including topical and oral medications. But it’s hard to know how well the treatments work because in many cases the condition simply resolves on its own.
If you have sudden and dramatic hair loss, you should see a physician, since this may indicate hormonal changes or other medical issues, for which there may be effective treatments. Stress may be a factor. Some dermatologists specialize in hair loss. For information about androgenetic alopecia—better known as male- or female-pattern hair loss—see Hair Loss: What Might Help (and What Probably Won’t).
Q: Can any dietary supplements reverse gray hair?
A: Don’t count on them. The marketplace is filled with supplements promising to banish gray hair, including ones containing the enzyme catalase (along with herbs, minerals, and a variety of other substances from green tea extract to ginseng to saw palmetto). But there’s no evidence that taking the enzyme orally can affect catalase levels in the hair follicle (assuming the enzyme even survives the stomach’s acidic environment and is then absorbed).
And though there are studies, mostly in Indian journals, linking premature gray hair (before ages 20 to 30) with nutrient deficiencies, such associations do not equal causation and don’t mean that any of these other ingredients will prevent or reverse gray hair, especially in older adults.
In recent years, the Federal Trade Commission has taken action against several marketers of these supplements, including GetAwayGrey, Go Away Gray, Rise-N-Shine, and Grey Defence, prohibiting them from making misleading claims. But these supplements often resurface with the same ingredients under different names such as BoniHair, and there are plenty of other gray hair supplements, such as Anti Gray Hair 9000 and Gray Hair Rescind, that continue to make bold, unproven claims.
Q: Is hair analysis valid?
A: Promoters of hair analysis claim that the test can detect nutritional deficiencies and various medical conditions. They then typically sell dietary supplements to correct whatever problem is supposedly revealed. But hair analysis cannot diagnose diseases. And though hair has some minerals (but no vitamins), there’s no practical value in measuring them since hair mineral levels do not reflect blood or tissue levels.
In fact, certain minerals in hair can be influenced by your age, the thickness of your hair, what shampoo you use, whether you use hair dye, and even the season, according to Dr. Stephen Barrett, founder of Quackwatch.org, which calls commercial hair analysis “a cardinal sign of quackery.” Plus, there are no standards for what the levels should be. Even if hair did reflect nutritional status, the hair sampled could be months or even years old, so it wouldn’t be a snapshot of your current status.
Hair analysis has some sanctioned uses, however: For instance, forensic scientists may check hair samples for poisoning from arsenic and other substances, including mercury and lead. Hair analysis can also be used to detect drugs, such as opiates, cocaine, and marijuana.
Q: Does hair continue to grow after death?
A: Hair grows according to a genetic program (hormones also are involved), about half an inch a month; each hair grows for two to six years. It’s a myth that hair continues to grow on a dead body, however—though the strands may appear to lengthen as skin dehydrates and shrinks. For hair to continue to grow, the follicles must be alive and cells in the body must produce hormones.
This article first appeared in the UC Berkeley Wellness Letter.
Also see 6 Things to Know About Gray Hair.