黑头是一种开放性粉刺，常与外界的空气、粉尘相接触，多发生于脸部、后背、前胸等。露在粗大毛孔外部的黑点，挤出后成条状，或有黑色的头部。

皮脂腺分泌的油脂本身可以滋润肌肤，当毛孔充满多余的油脂，毛孔被角质化的表皮细胞以及皮屑阻塞，油脂无法顺利排出，这些油脂和皮屑等混合物被外界空气氧化而形成黑头。

身体自身因素；阳光；清洁过度；用手挤压黑头部位；温度过高；熬夜过度；食用刺激性的食品。

A comedo is a clogged hair follicle (pore) in the skin. Keratin (skin debris) combines with oil to block the follicle. A comedo can be open (blackhead) or closed by skin (whitehead), and occur with or without acne. The word comedo comes from Latin to suggest the worm-like look of a blackhead that has been secreted. The plural of comedo is comedones.