Hello, You are suffering from rashes and bruises on lips after oral sex on your partner. The rash takes a couple of days to disappear. It can be due to perioral dermatitis, you can take a course of antibiotics like Doxycycline. Applying a thin layer of topical ointment Elidel on the rash may help. Make sure that it does not go inside your mouth. Your partner may be using some beauty product, douche or lotions to which your skin type is allergic and hence you may be getting the symptoms. Find out the ingredients of the products. Always use herbal products or water based products that are not perfumed / scented. STIs can be transmitted through the oral route. STIs that commonly spread through oral routes are herpes, syphilis, gonorrhea, chlamydia, genital warts, etc. You and your partner are suggested to get STD tests done to stay on the safer side. If report is positive you will be treated with antivirals / antibiotics. After oral sex you should maintain oral hygiene. Gently brush your teeth, gums and tongue as well. Rinse your mouth with a good mouth wash or warm salt water. Gargle with warm salt water. Avoid sugary products and quit smoking. Avoid oral sex if you have rash around your lips. Avoid it if you have sores or ulcers in your mouth or around your lips. Stay away from addictions if any. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Nupur K., General & Family Physician