Doxycycline is a tetracycline antibiotic. It fights bacteria in the body. Doxycycline is used to treat many different bacterial infections, such as acne, urinary tract infections, intestinal infections, eye infections, gonorrhea, 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. Some forms of doxycycline are used to prevent malaria, to treat anthrax, or to treat infections caused by mites, ticks, or lice. Doxycycline may also be used for purposes not listed in this medication guide.