Whether you spend a serious chunk of your morning styling your hair or roll out of bed and hope for the best, you might think of your mop as something decorative—but the locks on your head can actually tell you a lot about your internal health. 

We tend to associate shiny, vibrant, long hair with health—and there’s actually good reason for doing so, according to dermatologist Marisa Garshick, M.D., of MDCS Dermatology. Meanwhile, when hair is lackluster, dry, brittle, and falling out, it can sometimes indicate an underlying health issue. “These changes can reflect certain medical conditions such as those related to hormones, genetics, or thyroid changes, or be the result of certain medications, among other possibilities,” she says. 

Here’s what to know about how hair works—and what yours might be trying to tell you about your health.

Fast Facts About Hair

Most of us have hair and take a significant time out of each day to brush and style it, yet we don’t really take the time to think about what it really is—and how it actually grows.

Just like the skin is made up of three layers—the outer epidermis, the middle dermis (which is the layer hair grows out of), and the deeper hypodermis—hair is also made up of three layers. “The inner layer is known as the medulla and is often absent in fine locks,” explains stylist Penny James, IAT-certified trichologist and owner of Penny James Salon in New York City. “The second layer is known as the cortex and makes up the bulk of our hair, and the outer cuticle, which looks like overlapping scales, protects the cortex from damage.” 

Our actual hair follicles, which our hairs grow out of, cycle repeatedly through phases of development, including the anagen (growth) phase, the catagen (regression) phase, the telogen (resting) phase and the exogen (shedding) phase. At any given time, approximately 90 percent of our hairs are in the growing (anagen) phase, according to Brendan Camp, M.D., another dermatologist with MDCS Dermatology. We also lose about 100 strands daily as follicles enter the resting and shedding phases. 

What Your Hair Can Tell You About Health

Here are six common signals your hair can send you about your health and wellbeing.

1. You’re stressed out

Along with stress and anxiety often comes hair shedding and thinning, notes Garshick, and the culprit is often a surge of the stress hormone cortisol. “When our cortisol gets too high it stimulates the sympathetic nervous system and adrenal glands,” she says. One of the not-so-fun results: hair loss.

Of course, better managing stress is the best way to help your mane get back into balance—but, in the meantime, Garshick recommends taking a vitamin B complex supplement. “Riboflavin, biotin, folate, and vitamin B12 deficiencies have all been associated with hair loss,” she says. “If you are deficient, supplementing with them can help strengthen and support growth.”

Read More: 9 Signs You’re Vitamin B12 Deficient

She also recommends trying herbs like ginseng and ashwagandha, which can help the body cope with stress.

2. Your hormones are out of whack

Hormonal changes can also impact the hair. While this can sometimes be genetic or age-related, in women, it can also be due to a condition known as polycystic ovarian syndrome (PCOS), a hormonal disorder that affects as many as five million women of reproductive age in the U.S. and involves insulin resistance and an imbalance of male reproductive hormones, per the Centers for Disease Control and Prevention (CDC). Common symptoms of PCOS include scalp hair loss, as well as excessive hair growth in other areas, acne, and menstrual irregularities, Garshick says.

Treatment often involves a variety of lifestyle changes as well as medications to support hormonal balance and metabolic function.

3. You have alopecia areata

Hair loss in well-defined patches may signal a condition called alopecia areata, a common autoimmune disease that affects an estimated 147 million people worldwide (mostly adults between 30 and 60), per the National Alopecia Areata Foundation. “This condition occurs when inflammatory cells attack the hair follicle and weaken it so that hair is lost,” says Camp. “A board-certified dermatologist can help patients address this condition with in-office treatments and prescription medication.”

4. You have an underlying thyroid issue

Thinning hair and/or strand loss may be a feature of an overactive or underactive thyroid, notes Garshick. “The hallmarks of thyroid conditions include hair thinning and loss, as well as dryness and brittleness,” she says.

Read More: 7 Foods That Are Good For Your Thyroid

If you are noticing these changes, Garshick recommends having your thyroid levels checked by your primary care provider. If you are already on medication for a thyroid condition, inquire about adjusting your medication accordingly. “Beyond that, you can speak with a board-certified dermatologist to discuss other options to help strengthen and support the hair growth process,” she adds. 

5. You’re Pregnant Or just had a baby

The reason why so many pregnant women have thick, shiny hair: good ol’ pregnancy hormones, says Garshick. Unfortunately, a shift occurs after they give birth. “Because of postpartum hormonal changes, it is normal to experience a sudden hair shedding about two or three months after delivery,” she says. “Generally this phenomenon is self-limited and improves over the subsequent six to 12 months.”

6. You’re not getting the nutrients you need

A healthy, balanced diet is paramount to overall wellbeing, and falling short on your nutrition can absolutely impact your hair. 

“Any reductions in protein, carbohydrate, or overall caloric intake have all been associated with hair loss,” Garshick says. Since a variety of vitamins and minerals contribute to scalp and hair health, a diet lacking in the full array can contribute to brittleness, hair loss, and overall lackluster locks.

Crash diets or strict regimens that involve cutting out entire food groups are some of the biggest culprits, notes Garshick. To help facilitate regrowth, she recommends following a nutrient-rich diet filled with vitamins A, B, C, D, and E. When in doubt, a credentialed nutritionist can help you identify any shortcomings in your eating habits. (Click here to set up a free consultation with one of The Vitamin Shoppe’s nutritionists.)