Half of the redness and swelling in the urethra may be caused by improper sex, urethritis, paruresis and other factors. 1. Improper sex life: If you are too hard during sex and accidentally touch the urethra, it may cause half of the urethra to appear red and swollen. 2. Urethritis: If pathogenic bacteria accidentally invade the urethra, an inflammatory reaction may occur. The stimulation of local inflammation may lead to the symptoms of redness and swelling of one half of the urethra, which is often accompanied by abnormal urethral secretions, painful urination, urinary urgency, frequent urination and other manifestations. 3. Paraurethritis: Inflammatory changes mainly caused by pathogens attacking the paraurethral glands may lead to congestion and edema in the urethra, symptoms such as urinary urgency, frequent urination, painful urination and rash. If there is redness and swelling in half of the urethra, you should consult a doctor in time to avoid further development of the disease.