There are many reasons for a hard bump on the back of the foot and feel itchy, the more common reason for mosquito bites, accompanied by redness and swelling, may also be caused by disease factors, common diseases include: 1, allergies on the back of the foot: skin allergies on the back of the foot may lead to eczema or dermatitis, scratching with your hands when itching, can lead to a gradual increase in redness and swelling of the lesions. You can apply topical anti-itch medication under the guidance of a professional doctor, such as Denide ointment, Mometasone furoate ointment, etc. Itching can be serious oral desensitization drug therapy, such as loratadine, cetirizine, etc.; 2, infectious molluscum contagiosum: infectious skin disease caused by viral infection, manifested as papules or nodules, the top depression, red and itchy around. The preferred treatment is wart clamping, as well as drug therapy, physical therapy, etc. The actual fact is that you will need to maintain good personal hygiene in your daily life, to ensure that your feet are clean and dry, to avoid scratching and stimulating to aggravate your condition.