A lot of small bubbles on the penis, sometimes itchy but not painful may be allergic dermatitis, penile eczema, sexually transmitted diseases and other causes. 1. Allergic dermatitis: If you come into contact with allergic substances, such as fiber underwear, poor quality toiletries, etc., it may prompt a local allergic reaction, causing a lot of small bubbles on the penis, and is accompanied by itching, erythema and other uncomfortable symptoms. 2. Penile eczema: if a lot of sweating is not cleaned in time or the underwear is not breathable, it may induce penile eczema, there are a lot of small bubbles on the penis, and there will also be different degrees of itching symptoms. 3. Sexually transmitted diseases: when the male patient suffers from syphilis, warts and other transmissible sexually transmitted diseases, may also lead to the phenomenon of the penis grew a small bubble, and accompanied by itching and other uncomfortable symptoms. Men who have a lot of small bubbles on the penis, sometimes itchy but not painful, should immediately go to the hospital urology department to check, diagnose the condition, under the guidance of the doctor active treatment.