Whether we’re contending with a clogged shower drain or seeing more strands on our pillow than usual, we’ve all wondered whether our hair loss is normal. This guide will help you determine whether your hairline is really at risk.

How Hair Growth Works

The hairs on our head (and the rest of our bodies) are constantly moving through a three-phase cycle, in which our hair follicles sprout new hairs, rest, and then prepare to replace existing hairs with new ones.

During the anagen phase, our hair follicles produce a hair shaft. Then, during the catagen and telogen phases, they reset and stop growth to prepare their stem cells to start the next hair.

It takes any given hair years to move through the full cycle—and different hair follicles pass through different phases at different times.

“Normally, 80 to 90 percent of our hair is growing while 10 to 20 percent is ‘resting,’” explains Erum Ilyas, M.D., a board-certified dermatologist at Montgomery Dermatology in Pennsylvania.

What Normal Hair Shedding Looks Like

Though we’d all like to keep as many hairs on our heads as possible, our hair’s natural cycle means it’s completely normal to lose some strands every single day.

In fact, according to The American Academy of Dermatology, most people lost between 50 to 100 hairs a day. (This is known as ‘shedding,’)

That may seem like a lot, but fear not. “This is a very small amount of hair compared to the vast number of hair follicles humans have on their scalp, which averages around 100,000,” says Hal Weitzbuch, M.D., M.S., F.A.A.D., dermatologist and founder of hair line JuveTress.

Normal Shedding vS. Abnormal Hair Loss

In normal hair shedding, new hair grows in as the old strands fall out, so you don’t notice any thinning.

However, true hair loss occurs when the normal hair growth-shedding cycle is disrupted or the hair follicle itself is destroyed, according to the Mayo Clinic.

Common Causes Of Hair Loss

Most often, abnormal hair loss stems from hormonal and autoimmune issues. “Hair follicles are highly sensitive to changes in signaling from estrogen, prolactin, cortisol, and the thyroid hormones,” Zembroski explains.

That’s why extreme stress has been implicated in hair loss. “Elevated cortisol [a stress hormone] blocks thyroid hormones from influencing hair follicle activity,” says Zembroski. This reduces hair growth, causing hair to become brittle and thin out.

Related: Could You Have A Thyroid Issue?

Hair loss is also common in women who have estrogen dominance (too-high levels of estrogen and too-low levels of progesterone). This imbalance again affects thyroid function, and thus hair follicle activity.

Meanwhile, women diagnosed with polycystic ovarian syndrome (PCOS) often deal with hair loss related to excess testosterone.

Autoimmune dysfunction can also affect hair in multiple ways. In alopecia areata, which is marked by patchy hair loss, for example, “immune cells attack the rapidly growing cells in the hair follicles,” Zembroski explains. In Hashimoto’s disease, another autoimmune condition, though, the immune system spurs hair loss by attacking the thyroid.

Hormone and immune issues aside, seasonal shifts can also impact our hair. During shorter, darker winter days, we produce higher levels of melatonin (the ‘sleep hormone’), which can cause hair to move from the growth phase to the resting phase—and eventually into the shedding phase.

Signs Your Hair Loss Is Abnormal

Though it can be challenging to pinpoint whether you’re experiencing typical hair shedding or irregular hair loss, there are a few signs to look out for.

1. Your Eyebrows Are Thinning

Believe it or not, issues with hair loss on your scalp can also affect your eyebrows.

According to functional medicine specialist, clinical nutritionist, and author of REBUILD, Robert Zembroski, D.C., D.A.C.N.B., M.S., thinning of the lateral third of your eyebrows (the ends of your eyebrows, farthest from your nose), in particular, often signals true hair loss.

In this case, hair loss may be associated to thyroid issues—specifically hypothyroidism. “In hypothyroidism, the thyroid gland does not produce the amounts of thyroid hormones needed for normal physiological processes in the body, including healthy hair,” explains Zembroski.

2. The Part In Your Hair Looks Different

“The most common sign of abnormal hair loss in women is a widening part,” says Weitzbuch.

Take a look when combing or styling your hair. Can you see more of your scalp than usual? Does your part seem wider? If so, you may be dealing with hair loss related to imbalances in female sex hormones.

3. Your Hair Line Is Thinning Or Receding

This pattern of hair loss, known as ‘male pattern baldness,’ is the most common type of hair loss men experience.

“Men most often notice a receding hair line and a thinning spot on the top of the head,” says Weitzbuch.

While this type of hair loss can begin at any age, the likeliness of it setting in grows more likely as men get older. “Genetics, hormones, environment, and health factors all play a role,” he explains.

Male pattern hair loss is also the type of hair loss many women with PCOS face.

4. Some Parts Of Your Hair Feel Thicker Than Others

When autoimmune issues—particularly alopecia areata—are at play, hair tends to fall out in random but distinct clumps.

If you notice small, disc-like spots where hair is incredibly thin—or has fallen out completely—consider it a possible sign of autoimmune trouble.

5. You’re Shedding A LOT

While it is normal to notice shedding every day, losing more than 100 strands of hair per day is considered ‘excessive shedding.’

Look out for an unusually high number of hairs on your pillowcase, in your hairbrush, or atop the shower drain. Typically, this type of all-around excessive shedding is caused by stress—and the elevated cortisol levels that come along with it.

6. You Hair Feels Brittle And Thin

If your individual hairs feel brittle, dry, and thinner than usual, there may be more at play than just needing to deep condition more often.

In fact, these hair changes may indicate thyroid issues, specifically hypothyroidism. “Low levels of thyroid hormones can cause dry, brittle, coarse hair and reduced hair cell growth,” explains Zembroski.

Look out for dull, stringy strands—and a ponytail that lacks its usual oomph.

How To Revive Your Locks

If you’re experiencing unexplained hair loss, make an appointment with your doctor. They’ll help you investigate whether a hormone- or immune-related condition might be messing with your mane.

From there, your doctor will help you address the root cause of your hair woes and recommend a treatment for supporting healthy hair in the meantime.

Related: The 6 Best Supplements For Healthy Hair

Of course, living a healthy lifestyle is also hugely important for overall healthy hair. Make sure you’re getting your fill of nutrients like protein (especially collagen) and vitamin D, which play key roles in hair growth and strength. Managing stress, minimizing your use of hot styling tools, and limiting super-tight hairstyles can also help your locks thrive.

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