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Mild swelling can occur after masturbation which should subside within 48-72 hours. Avoid further manipulation. If the swelling/bulge is persistent, or if symptoms are getting worse, or if you develop pain or any discharge, consider visiting your doctor/healthcare provider for further examination and evaluation to look for the underlying cause. Treatment as needed (based on examination findings and investigations results) would be started to help you control the symptoms. Be in regular monitoring and follow-up with your treating doctor/healthcare provider and report any new/abnormal symptoms immediately.
Take care.