Doxycycline is a drug that you may need to use to treat infections caused by the presence of bacteria in the body. Doxycycline can make your skin more sensitive to sunlight. Make sure you avoid staying in the sun for too long and wear protective clothes plus sunscreen when you have to. Doxycycline can cause other side effects and you need to be aware of the possibility. The following mild side effects are sometimes possible: vaginal itching, vomiting, sore mouth, stomach upset, mild nausea, diarrhea, swollen tongue, trouble swallowing, as well as sores or swelling in your rectal or genital area. More serious side effects are quite rare and will need to be reported to your health care provider right away. Make sure you inform your doctor of the following side effects that are considered to be serious: itching, skin rash, blurred vision, severe headache, yellowing of the skin or eyes, difficulty breathing, confusion, decreased urination, vomiting, upset stomach, redness of the skin, dark-colored urine, stomach pain, and loss of appetite. Never share your doxycycline with other people to whom it was not prescribed, as this may lead to unpredictable effects in those people.