The most common causes are:

• irritants: neglected hygiene and tight foreskin (particularly in young boys) lead to irritation by smegma (a cheesy substance secreted under the foreskin).
• seborrhoeic dermatitis: an inflammatory rash of uncertain cause that is commonly seen on the scalp, behind the ears and in the skin folds.
• thrush (candida): although this infection is probably over-diagnosed by doctor and patient.
• contact allergy: latex and additives used in rubber manufacture (eg condoms) and constituents of skincare products (used by the patient or partner).
• balanitis xerotica obliterans (BXO, also termed lichen sclerosis): this condition primarily affects the foreskin, leading to loss of skin colouration, scarring and tightness of the foreskin, and phimosis (inability to pull the foreskin back behind the glans), which may require circumcision. Involvement of the opening of the urethra (urine tube) can lead to irritation and burning. Surgery might be needed to prevent a stricture (narrowing) in the urethra. Steroid creams may help the irritation but patients require long-term follow-up to prevent recurrence.
• balanitis circinata: a skin manifestation of Reiter's syndrome, in which the patient also has arthritis (often of the knees), urethritis (inflammation of the urine tube in the penis) and conjunctivitis (red eyes).
• generalised skin conditions: these can also affect the penis, including: lichen planus, psoriasis, erythema multiforme, erythema fixum (particularly caused by tetracycline antibiotics), erythroplasia of Queyrat (a rare, pre-cancerous skin condition).
• diabetes.

Balanitis in young boys is usually associated with a tight foreskin that cannot be pulled back behind the glans (phimosis). Phimosis leads to deficient hygiene and persistent contact of urine and smegma with the skin of the glans. Straightforward cases usually respond to antibiotic ointments but recurrent cases require investigation to exclude urinary tract infection.

Occasionally, irritation and swelling of the glans can be due to paraphimosis ('Spanish collar'), caused when a tight foreskin is retracted down the shaft behind the glans. The tightness around the shaft slows the venous drainage of the end of the penis, and the glans swells, which tightens the paraphimosis further, making the foreskin virtually impossible to retract. Ultimately, the restriction can interfere with the blood supply to the glans and urgent medical treatment is required. Often the foreskin can be returned to its normal position under sedation, but, if not, circumcision is required.