Doxycycline may cause heightened risk of sunburn.
 When bacteriologic testing indicates appropriate susceptibility to the drug, doxycycline may be used to treat these infections caused by Gram-positive bacteria:Upper respiratory infections caused by Streptococcus pneumoniae (formerly Diplococcus pneumoniae)Skin and soft tissue infections caused by Staphylococcus aureus, including methicillin-resistant Staphylococcus aureus infectionsAnthrax caused by Bacillus anthracis infectionWhen penicillin is contraindicated, doxycycline can be used to treat:Syphilis caused by Treponema pallidumYaws caused by Treponema pertenueListeriosis due to Listeria monocytogenesVincent's infection caused by Fusobacterium fusiformeActinomycosis caused by Actinomyces israeliiInfections caused by Clostridium speciesDoxycycline may also be used as adjunctive therapy for severe acne
In Canada, in 2004, doxycycline was considered a first-line treatment for chlamydia and non-gonococcal urethritis and with cefixime for uncomplicated gonorrhea

