I guess you are referring to the brain stimulation rather than activity. If you actually think that it decreases the brain activity than you are unaware of the fact that watching porn helps many in increasing the brain activity and repairing sex life in many cases as well. When you do an actual p....

Take antantibiot and consult a surgeon nearby you 

It's safe, considering you both are disease-free. Also, you'd probably want to consider your birth control status. If you're using condoms, the penis can shrink and the condom can slip off, exposing you both to disease and you to becoming pregnant if his semen seeps into your vagina. Me and my ma....