The marks left by mosquito bites are caused by insect bite dermatitis, the red marks caused by dermatitis can generally be eliminated in about 7 days; if it is the black marks caused by post-inflammatory hyperpigmentation, it may take about 3 months to eliminate. Insect bite reaction is a dermatitis skin disease caused by insect bites, the bite may appear red, swollen, blisters and other symptoms. Usually, red marks caused by inflammation will subside in about 7 days. If it is a black mark caused by post-inflammatory hyperpigmentation, it often takes longer, and usually may take about 3 months to subside. Therefore, it is impossible to generalize how long it will take to get rid of the marks left after being bitten by mosquitoes. For those who have been bitten by mosquitoes and left with marks, it is recommended to go to a regular hospital and consult with a doctor about the matter.