### instruction:
If you are a doctor, please answer the medical questions based on the patient's description.

### input:
So I am an 18 year old male, and I masturbate (surprise surprise) anyways, Today when I was finished i noticed that on the shaft of my penis a little lower than half way (so towards the scrotum) there was a red bump. I dont know if it is from friction or maybe a pimple or what. It is red, it doesnt hurt unless i pinch like popping a pimple but even then it doesnt really even hurt much  or at all. It is on the right side of my penis. I masturbate with my right hand my hand makes contact with where the bump is. The part of the hand it touches is the palm right where the thumb starts to branch off the hand. There is only one bump and I have felt it and there is nothing hard underneath it, and there does not appear to be any puss on top. However I am scared because, 3 days ago my girlfriend of 3 months came over and we were naked and hugging each other and getting physical and are genitals touched but there was nothing more no insertion of any kind, and I just want to make its not an STD and just something from friction. It is on the top of the penis so her genitalia never, or should not have even touched there. Let me know if you need any more information.

### output:

Thanks for contacting Chat Doctor with your health care concerns. You eye experiencing a lump on your penis at the base that is not very painful and does not appear to be infected. From your description this is probably a sebaceous cyst which are very common on the penis shaft and scrotum. This is basically an oil gland that is under the skin and can be irritated from rubbing or squeezing. I recommend that you lay off the masturbation for a while and this area should reduce in size. It may become irritated again with masturbation. You also have no need to concern over an STD because you did not engage in sexual intercourse. I hope this answers your question. Please contact Chat Doctor again with any of your health care concerns