5. Yellow dandruff: Seborrheic dermatitis
Though it mostly occurs in infants, seborrheic dermatitis—crusty, oily patches of yellow-white scales on the scalp—can afflict adults, too. “Like dandruff, seborrheic dermatitis is caused by a microbe that lives on our scalp,” note the experts at Head and Shoulders. “It’s called Malassezia globosa. About half the population is sensitive to a substance the microbe makes called oleic acid. Typically, this leads to dandruff—but among people who are very sensitive to oleic acid, it can trigger seborrheic dermatitis.” The National Eczema Association also cites stress, hormonal changes, and harsh detergents as common triggers for sebhorreic dermatitis.
The good news? “This condition is very treatable,” says Dr. Marguerite Germain of Germain Dermatology in Charleston, South Carolina. Medicated shampoos, creams, or lotions can loosen the scales and alleviate that pesky itch.
6. Itchy scalp: Zinc deficiency
“Hair needs a mixture of vitamins, minerals, and trace elements to grow. Zinc is one of these essential trace elements,” according to the experts at Philip Kingsley. That’s because “zinc helps our bodies to process carbohydrates, fats, and proteins–the building blocks of hair.”
As a result, having low levels of zinc could cause an otherwise healthy scalp to become persistently itchy, according to a 2015 study published in the Journal of Clinical and Investigative Dermatology.
7. Fine, dry hair: Hormonal changes
“Hormonal imbalances can definitely be a contributing factor to a patient’s hair health,” says Robin Levin, M.D., a board-certified dermatologist based in New Jersey.
For example, a change in birth control may trigger a new level of hormones your body isn’t quite used to—which can lead to changes in your hair texture as well. “We can tell when someone is on a new type of birth control because it can make their hair finer, drier, and less shiny,” celebrity colorist Rita Hazan, owner of the Rita Hazan Salon in Manhattan, told Oprah.com.
8. Hair loss: Iron deficiency
Ferritin is a blood cell protein that contains iron, according to the Mayo Clinic. And optimal levels are needed to maximize your hair’s “anagen,” or “growing,” phase, the experts at Philip Kinglsey note. When your body doesn’t have enough of the stuff, you can become iron deficient anemic, which causes tiredness, weakness, and hair loss. So, if you’re seeing more hair on your brush than usual, slate more iron-rich foods—like spinach and grass-fed beef—into your diet.
9. Or a thyroid condition
The moment you start to notice thinning hair, along with brittleness, head to your doctor for a blood test to check out your thyroid levels. Hormones produced by the thyroid are essential for the development and maintenance of hair follicles. So if your locks are looking less luscious, that could be the result of any number of endocrine disorders, such as hypothyroidism, hyperthyroidism, or parathyroid disorder, according to a 2013 study in the International Journal of Trichology.
10. Or medication side effects
As Lynne Goldberg, director of the Hair Clinic at Boston Medical Center, told The Boston Globe, there are several medications that may contribute to temporary hair loss as well, including antidepressants, anticoagulants (blood thinners), and certain steroids.
Though much of the reasoning is still unknown, these medications may interfere with the normal cycle of scalp hair growth, causing the follicles to go into their “telogen,” or “resting,” phase and fall out too early. The good news is that this particular form of hair loss is largely reversible. If you think one of your medications may be contributing to irregular hair loss, talk to your doctor.