A penis sore can occur due to injury from tight clothing or sex, or due to poor hygiene. It can also occur due to an allergy to clothing fabric or hygiene product, leading to dermatitis. There are infections that can also cause sores, like syphilis, genital herpes, or even penile cancer. Some men may also experience additional skin changes, like small lumps resembling genital warts.
Because there are so many causes for them, penis sores should be assessed by your doctor. Your doctor may inspect and palpate the lesions, review the history of your symptoms, and order testing to rule out infection. Treatment will depend on the underlying cause, and may include healing ointments, antibiotics, antifungals or antivirals. If the sore is caused by a sexually-transmitted infection, it is important that your sexual partner also seeks treatment.
The most common causes of sores on the penis are:

1. Skin irritation
Some people may experience skin sensitivity to clothing fabric or hygiene products, which can trigger redness, skin peeling, open sores, itching and burning.
Skin irritation can also occur due to friction from clothing or sex. Poor hygiene may also lead to irritation, as accumulated sweat, oil and microorganisms can cause a penile inflammation called balanitis.
How to heal: If irritation is allergy-related, you should avoid contact with the triggering allergen. You can take antihistamine pills or creams to relieve symptoms. Moisturizing creams may also help to heal affected skin. Balanitis is treated with corticosteroid creams, antifungals or antibiotics. When treated correctly, the lesions may take about 1 week to heal.
2. Genital herpes
Genital herpes is one of the most common causes of sores on the penis. Is caused by the herpes simplex virus, which can be acquired through contact with a person with active, open sores. Genital herpes is characterized by the appearance of small blisters that cause pain and burning. Check-out the common symptoms of genital herpes.
How to heal: Treatment for genital herpes is prescribed by the doctor, who may advise the use of antiviral medication like acyclovir or famcyclovir in pill or cream form. These help to reduce virus replication. Other creams or gels with anesthetic properties, like lidocaine, may help to relieve uncomfortable symptoms like pain and burning.
Learn more about other causes of lumps or bumps on the penis.
3. Syphilis
Syphilis is an infection caused by Treponema pallidum bacteria. It causes a painless ulcer that appears about 3 weeks after initial exposure. This infection is often transmitted through unprotected sex from an infected partner. If left untreated, syphilis can lead to more advanced stages of infection, like secondary or tertiary syphilis. Read more about how to recognize symptoms of syphilis.
How to heal: You should see your doctor if you suspect you have symptoms of syphilis so that appropriate treatment can be initiated promptly.
4. Other STIs
Other sexually-transmitted diseased, or STIs, can cause open sores, like lymphogranuloma venereum (LGV), donovanosis or HPV. Perianal lesions that occur internally, like urethritis, can cause pain, yellow or lighter discharge. These sores can occur due to bacteria like Neisseria gonorrhoeae, which causes gonnorhea.
How to heal: Once an STI is diagnosed, you should proceed with treatment as prescribed by your doctor. Many times it consists of a course of antibiotics, while HPV treatment involves cauterization of the lesions. Learn more about the treatment of HPV.
5. Autoimmune disease
Some autoimmune disease can also trigger the appearance of penile and genital sores, which is the case with Behcet's disease, pemphigus, lichens planus, Crohn's disease, Reiter's disease, erythema multiforme and dermatitis herpetiformis. With these illnesses, lesions will often appear in other areas of the body as well. It is also common to experience systemic symptoms, like fever, fatigue or weight loss.
How to heal: Diagnosis and treatment of autoimmune diseases are often done under the supervision of a rheumatologist or dermatologist. Treatment consists of medications, like immunosuppressants or corticosteroids, that regulate immunity and improve symptoms.
6. Cancer
Penile cancer is very rare and characterized by the growth of a tumor that can occur on the shaft or scrotal skin. It can lead to the appearance of sores, nodules, or changes to skin color or texture. This type of cancer is more commonly seen in men over the age of 60, but it can also occur in younger men who are smokers or do not practice appropriate hygiene. Ensure you are familiar with the most common signs and symptoms of cancer.
How to heal: The treatment for cancer is directed by an oncologist and urologist, and may involve the use of medications, surgery to remove affected tissue and/or chemotherapy or radiation therapy. Treatment modalities will vary depending on the cancer stage and lesion severity.