脱发，是因人缺铁和蛋白质头发就会变黄、分叉；缺植物油、维生素A、蛋白质和碘时头发会发干、无光泽、容易折断；缺维生素B群时会出现脂溢性皮炎和头发脱落现象。脱髪的现象主要发生在中老年人、病患者、天生遗传、保养失当的人身上，受到辐射的影响也会脱发。

随着生活节奏的加快，熬夜 、失眠、精神压力的增加，都会引起发量和头皮油脂的剧烈变化。

Hair loss, also known as alopecia or baldness, refers to a loss of hair from the head or body. Baldness can refer to general hair loss or male pattern hair loss.

Hair loss and hypotrichosis have many causes including androgenetic alopecia, fungal infection, trauma (e.g., due to (trichotillomania), radiotherapy, chemotherapy, nutritional deficiencies (e.g., iron deficiency), and autoimmune diseases (e.g., alopecia areata). Hair loss severity occurs across a spectrum with extreme examples including alopecia totalis (total loss of hair on the head) and alopecia universalis (total loss of all hair on the head and body).