Men who have sex after the root of the penis is so itchy to consider may be related to allergies, bacterial and fungal or trichomonas and other infections and sexually transmitted diseases. 1. Allergy: If you use a condom during sex, a few people may have an allergic reaction because of the condom, then the external genitalia in addition to itching, there may also be red spots, redness and swelling of the symptoms, considering that it may be a contact allergy. 2. Bacterial, fungal or trichomonas infections: If the woman in the same room suffers from bacterial vaginitis, fungal vaginitis or trichomonas vaginitis infection, the patient in sexual contact, may lead to the patient is also infected, appearing glans erythema, erythema and itchy, and may be accompanied by localized pain, or localized white secretion increase and so on. 3. Sexually transmitted diseases: such as chlamydia, syphilis spirochetes, gonorrhea and other infections, the patient may appear itching, localized lesions, resulting in localized skin ulceration, pus and oozing and so on. If a man has an itchy penis root after sex, it is recommended to consult a doctor in time to find out the cause of the disease and timely treatment.