Hair thinning is a mysterious beast; too often, there’s no simple explanation for why it occurs. When your hair starts thinning in your twenties or early thirties, it can be quite upsetting. The causes can be complex, ranging from underlying health issues to medications and environmental stressors. To shed light on the issue, we asked board-certified dermatologists and plastic surgeons to explain some of the most common causes of hair thinning—and what you can do about it.
The Root Cause of Hair Thinning, Explained
“Hair loss is extremely complicated,” states Monroe, LA, dermatologist Janine Hopkins. “Just the consultation can take more than half an hour because we need to go over a patient’s lifestyle, habits, medications, and any underlying health issues. It varies according to their gender, age, hormones, stress level, and hair practices.”
Another key factor is genetics. “Genetics play a large role,” says Tina Alster, MD, a dermatologist in Washington, D.C. One example: “If a person’s mother or father experienced hair loss, that person has a much higher risk of developing the same.”
When your hair begins to thin in your twenties, genetics may play a part. However, if your parents didn’t lose their hair at an early age, determining the cause can be difficult. “Hair thinning can sometimes feel like a mystery, especially when it’s caused by less obvious factors,” explains dermatologist Kally Papantoniou from Melville, New York.
However, one thing is universally true: if you find your hair thinning or shedding, you should be proactive and consult an expert. In such cases, a doctor may prescribe “oral or topical medications, or a combination of both,” according to plastic surgeon Daniel Crane, MD, of Delray Beach, FL.
For many people, hair thinning (a progressive decrease in hair density over time) or hair loss (large patches of hair falling out at once) can be caused by a combination of factors. “The majority of hair loss cases I see are multifactorial,” says Dr. Hopkins. “Like on a multiple-choice test, we find that ‘all of the above’ is often the right answer.”
Discover some of the most common causes of hair thinning and loss that may be affecting you.
Diet and Hair Thinning
Diet-related hair thinning can lead to a progressive decrease in hair density, which is generally undetectable at first.
“Nutritional deficiencies, such as low levels of vitamin D, iron, or biotin, can impact hair growth by disrupting the natural hair cycle,” Dr. Papantoniou says. “Eating a well-balanced diet rich in leafy greens, nuts, and fatty acids can often help address this.
“People rarely eat enough protein,” Dr. Hopkins explains. “And if someone is not getting enough nutrients in one area, it’s possible they’re also going to be low in things like iron and vitamin D.”
Medications and Hair Thinning
“Certain medications, such as Ozempic, blood pressure medications, or antidepressants, may also contribute to hair thinning by affecting the hair growth cycle,” according to Papantoniou. “If you suspect this might be a factor, discussing alternatives or adjustments with your healthcare provider could help.”
Dr. Hopkins recommends that patients taking weight loss medicines consult with a dietician to reduce any side effects.
Scalp Health and Hair Thinning
For your hair to grow strong and healthy, the scalp must be in good condition. “Your scalp health also plays a critical role in hair thinning,” explains Dr. Papantoniou. “Scalp buildup, whether from styling products or untreated conditions like dandruff, can clog follicles and create an unhealthy environment for hair growth.”
Trauma and Stress Hair Loss
Stress-related shedding looks more like hair loss than thinning and is more sudden.
“Any major physiologic change, like rapid weight loss, can cause stress shedding, called telogen effluvium,” explains New York dermatologist Doris Day, MD. “This causes hair follicles to enter the resting phase prematurely and fall out.”
However, stress-related hair loss is not caused solely by rapid weight loss. “It can also be the result of physical illness, general anesthesia from surgery, and even childbirth,” explains Hopkins’s doctor. “If anything disrupts the supply chain in your body that permits hair development, the entire factory may shut down. Without the nutrients to generate, you’ll receive a subpar product in which hair weakens, thins, or doesn’t grow at all.
