A mark under the armpit may be caused by physiological factors, such as indentation caused by over-tightening of underwear, which usually requires no treatment; it may also be caused by pathological factors, which are commonly seen in post-inflammatory hyperpigmentation, atrophic lines and other diseases, and it is recommended that patients should be given general treatment, medication, physiotherapy and other ways to improve the condition according to the cause of the disease. 1. Physiological factors: such as underwear is too tight, underwear is too tight may cause underarms have strangulation marks, usually no treatment is needed, we recommend that patients wear the right size underwear, avoid too tight or too loose, in order to effectively eliminate strangulation marks. 2. Pathologic factors: (1) Post-inflammatory hyperpigmentation: post-inflammatory hyperpigmentation is usually secondary to the healing of certain inflammatory diseases, such as band psoriasis, linear lichen planus, linear moss, linear epidermal nevus of inflammation and other diseases, which may lead to the appearance of a line of marks in the armpit. It is recommended that patients pay attention to sun protection in daily life, can follow the doctor’s instructions for external use of hydroquinone cream and other drugs to lighten the pigmentation, if necessary, can be improved through laser treatment and other ways, the use of laser photothermal principle of melanin particles will be shattered, through the lymphatic circulation metabolism and thus play a lightening effect. (2) atrophic lines: also known as swelling lines, the disease occurs in pregnancy, obesity and other conditions, manifested as red, white alternating distribution, watermelon lines like cord-like lines, but also can cause the armpit appears a trace. The disease generally has no major impact on health, so there is no need for special treatment. If it affects the aesthetics, it can be alleviated and improved by laser treatment, local injection of fillers (such as hyaluronic acid, autologous fat, etc.) under the guidance of a doctor. Armpit traces may also be caused by other diseases, it is recommended that patients go to a regular hospital in time for a clear diagnosis, standardized treatment under the guidance of a doctor, do not use their own drugs and other ways to improve, so as not to cause serious adverse reactions.