Hi, A sebaceous cyst is caused due to infection of sebaceous glands in the skin. It can be managed conservatively by administering a course of appropriate antibiotics. If it is big and not responding to a conservative line of treatment, it needs to be excised by a minor surgical procedure. Doxycycline is a broad spectrum antibiotic that is used in the treatment of infections. Common side effects include diarrhoea, nausea, vomiting, red rashes on the skin, and an increased risk of sunburns. Adverse reactions like tooth discolouration, hemolytic anaemia and hepatotoxicity usually occur when high doses of the drug are administered or when taken frequently for a longer duration of time. Kindly take the medication as prescribed by your doctor and do the necessary follow-up as advised. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Ashakiran S, General & Family Physician