Hello, With reference to your query regarding that you were kissing your boyfriend and at that time your boyfriend had an unexpected and unaware nose bleed which stopped on it's own. However, you ended up with his blood in your mouth, but you did not swallow it, and you started worrying about this. You also stated that your boyfriend is currently ill with an infection i.e. penicillin. However you did not mention what kind of infection is he suffering from? Nose bleeding is medically known as "Epistaxis". It is common in children but can occur in adults if they are suffering from high B.P. Sometimes injury to the nose also results in nose bleeding. It can be light or heavy, and even if you are on some medication like anticoagulants. If the bleeding lasts for more than 30 minutes, it is better to get into A & E department as soon as possible. When the mucous membrane of the nose becomes dry due to an infection or cold weather or drying effect of central heating, then it gets inflamed or cracked and likely to bleed. As a first aid measure, you compress he nose above the nostrils for 10 minutes. Lean forward and start to breathe through the mouth. Still if the bleeding does not stop, you can get cauterization and pack the nose with ribbon gauze or a nasal sponge until the bleeding has stopped. Then your GP can remove them the next day and get it checked by the ENT specialist, who can do some investigations to find out the cause and treat it accordingly. In case you had his blood in your mouth, nothing will happen unless he is suffering from HIV infection and also if there is breakage of skin in your mouth. Try to clean your mouth with some antiseptic lotion and not to worry too much about this. In case if there is any blood you swallowed you might get nausea or vomiting. To allay any fear from your mind, if there is any change after this incidence, you can consult your GP who can examine you and give his valuable advice.Thank you.