There are many reasons why eyebrows fall out, first of all, eyebrows are also human hair, and like hair, there are different growth periods, namely the growth period, the regression period and the resting period. The hair in the regression and resting phases will fall off physiologically due to normal metabolism. Eyebrow hair can also fall out if there is excessive stress, endocrine abnormalities or severe malnutrition. There are also disease factors that can cause eyebrow hair loss. 1, contact dermatitis: contact dermatitis caused by contact with irritating cosmetics causes local vasodilatation of the skin, which can cause hair loss symptoms in severe cases. 2, seborrheic dermatitis: it is an inflammatory skin disease that manifests itself as oily skin sebaceous glands, erythema, oily scales, etc., some of which can be accompanied by itching, often recurrent, and the onset of the site if the eyebrows 3, bacterial or fungal infection: affect the growth of hair follicles will cause hair loss; 4, baldness: the main manifestation of the disease with limited patchy hair loss, may also involve the eyebrows, resulting in the loss of eyebrows; 5, scleroderma: characterized by limited or diffuse inflammatory changes in the skin, such as skin degeneration, thickening and fibrosis, the lesion skin parts of the hair will fall out; 6. Hypothyroidism: can involve the nerve, endocrine and other systems, affecting human growth and development, resulting in rough, brittle nails and hair, thus falling off; 7, syphilis: syphilis virus on the human skin, aorta, eyes, placenta, umbilical cord susceptibility, can be adsorbed to these tissues, causing the collapse of its blood vessels, local blood supply is blocked, followed by vascular inflammation, tissue necrosis, ulcers and other lesions. If the onset of the eyebrows, it will cause eyebrow hair loss; 8, leprosy: the causative agent is Mycobacterium leprae, the mode of action is to attack the skin, destruction of peripheral superficial nerves, is a chronic infectious disease, will lead to the outer third of the eyebrow hair loss. Physiological loss of eyebrows, generally improve lifestyle, such as strengthening nutrition, avoid overwork, maintain adequate sleep, etc., can generally be slowed. Pathological eyebrow loss requires a visit to the hospital to clarify the diagnosis of the primary disease in order to treat the problem.