Sudden red bumps on the thighs may be caused by allergies, folliculitis, insect bite dermatitis and other diseases that manifest as pimples. 1. Allergy: when some mosquitoes bite thighs or other allergens touch thighs causing hives, red bumps may appear, at this time you need to stay away from allergens in time, and timely medical attention, rub some ointment; 2. Folliculitis: some people who have been drinking alcohol for a long time or suffering from diabetes may have inflammation of the hair follicles, resulting in red bumps on the thighs, and accompanied by itching; 3. insect bite dermatitis: after being bitten by mosquitoes, erythema, papules, pimples and other symptoms appear due to localized toxin irritation. In the case of sudden red bumps on the thighs, in addition to the need for timely medical treatment, you also need to pay attention to a light diet, eat more fruits and vegetables.