Anyone can experience significant stress when their once-thick hair noticeably becomes sparser or thinner. In addition to genetics, female hair loss can result from various causes, including hormonal changes, nutritional imbalances and illness. Fortunately, treating an underlying condition responsible for the hair loss can restore hair to a healthy state. What are the three representative diseases that a dermatologist identified as causes of female hair loss?
▶Thyroid disease=Both hyperthyroidism and hypothyroidism interfere with hair growth. According to statistics from the Health Insurance Review and Assessment Service, women accounted for 82%, or about 590,000, of the approximately 720,000 patients with hypothyroidism in 2025, making it a common condition among women. The thyroid is a kind of body engine that regulates metabolism and manages the rate at which nutrients are converted into energy. Paradi Mirmirani, a dermatologist at Kaiser Permanente Medical Center in the United States, said, “When a thyroid problem causes the engine to overheat or shut down, the body prioritizes allocating resources to organs essential for maintaining life,” adding, “During this process, hair follicles abruptly stop the hair-growth phase and enter the resting phase, causing large amounts of hair to fall out.” Thyroid problems are accompanied by other systemic symptoms. Hyperthyroidism causes fatigue, weight loss and a pounding heartbeat, while hypothyroidism causes weight gain and a slower heart rate. The condition is easily diagnosed with a blood test, and once thyroid levels return to normal with medication, hair grows back over six to nine months.
▶Iron deficiency=When the body lacks iron, it cannot produce enough hemoglobin, the protein in red blood cells that carries oxygen, leading to iron-deficiency anemia. It is frequently observed in women with heavy menstrual bleeding or inadequate nutritional intake. Amy McMichael, a professor of dermatology at Wake Forest University in the United States, said, “When the body becomes deficient in iron, it prioritizes the energy previously used to grow hair for managing anemia,” adding, “Hair loss begins during this process.” When levels of ferritin, the body’s intracellular iron storage protein, fall below the reference level of 30 ng/mL, hair rapidly becomes thinner. Replenishing deficient iron through oral supplements or injections can restore hair condition within several months. A diet that includes iron-rich foods such as red meat, fish, legumes and leafy greens can also help.
▶Polycystic ovary syndrome=In addition to pregnancy and menopause, hormonal conditions such as polycystic ovary syndrome can cause hair loss. While this condition makes body hair grow more abundantly, it causes scalp hair to become thinner. This happens because excess male hormones, or testosterone, are converted into dihydrotestosterone, or DHT, which shrinks hair follicles. The condition should be suspected particularly when acne, irregular menstruation and weight gain occur at the same time. Treatment primarily involves medications that block male hormone receptors. Dr. Mirmirani said, “The earlier treatment begins, before thinned hair follicles completely degenerate and disappear, the greater the likelihood of regaining the original hair.” However, some treatments carry a risk of fetal abnormalities, so women who may become pregnant must consult a doctor.
▶Thyroid disease=Both hyperthyroidism and hypothyroidism interfere with hair growth. According to statistics from the Health Insurance Review and Assessment Service, women accounted for 82%, or about 590,000, of the approximately 720,000 patients with hypothyroidism in 2025, making it a common condition among women. The thyroid is a kind of body engine that regulates metabolism and manages the rate at which nutrients are converted into energy. Paradi Mirmirani, a dermatologist at Kaiser Permanente Medical Center in the United States, said, “When a thyroid problem causes the engine to overheat or shut down, the body prioritizes allocating resources to organs essential for maintaining life,” adding, “During this process, hair follicles abruptly stop the hair-growth phase and enter the resting phase, causing large amounts of hair to fall out.” Thyroid problems are accompanied by other systemic symptoms. Hyperthyroidism causes fatigue, weight loss and a pounding heartbeat, while hypothyroidism causes weight gain and a slower heart rate. The condition is easily diagnosed with a blood test, and once thyroid levels return to normal with medication, hair grows back over six to nine months.
▶Iron deficiency=When the body lacks iron, it cannot produce enough hemoglobin, the protein in red blood cells that carries oxygen, leading to iron-deficiency anemia. It is frequently observed in women with heavy menstrual bleeding or inadequate nutritional intake. Amy McMichael, a professor of dermatology at Wake Forest University in the United States, said, “When the body becomes deficient in iron, it prioritizes the energy previously used to grow hair for managing anemia,” adding, “Hair loss begins during this process.” When levels of ferritin, the body’s intracellular iron storage protein, fall below the reference level of 30 ng/mL, hair rapidly becomes thinner. Replenishing deficient iron through oral supplements or injections can restore hair condition within several months. A diet that includes iron-rich foods such as red meat, fish, legumes and leafy greens can also help.
▶Polycystic ovary syndrome=In addition to pregnancy and menopause, hormonal conditions such as polycystic ovary syndrome can cause hair loss. While this condition makes body hair grow more abundantly, it causes scalp hair to become thinner. This happens because excess male hormones, or testosterone, are converted into dihydrotestosterone, or DHT, which shrinks hair follicles. The condition should be suspected particularly when acne, irregular menstruation and weight gain occur at the same time. Treatment primarily involves medications that block male hormone receptors. Dr. Mirmirani said, “The earlier treatment begins, before thinned hair follicles completely degenerate and disappear, the greater the likelihood of regaining the original hair.” However, some treatments carry a risk of fetal abnormalities, so women who may become pregnant must consult a doctor.