Doxycycline is a tetracycline antibiotic. It fights bacteria in the body. Doxycycline is used to treat many different bacterial infections, such as urinary tract infections, acne, gonorrhea, and chlamydia, periodontitis (gum disease), and others. Doxycycline is also used to treat blemishes, bumps, and acne-like lesions caused by rosacea. Doxycycline will not treat facial redness caused by rosacea.