Question
Are his balls OK? I have given my bf a couple of blow jobs and sometimes his ball sac is big and really hangs down but the other day it was tight up against him and his balls felt smaller.
Answer
Short answer: Yes.
Long answer: I think so.
At least, what you have described is within normal behavior for men's balls. Sometimes they hang low, sway to and fro... Sometimes the scrotum pulls the testicles up tight against the body. There can be a few reasons why his body is doing this.
One might be because it's a little cool. Sperm are created and live inside the testicles. The normal body temperature is around 37°C but this is too hot for sperm. The balls normally hang low to keep them away from the body and keep them a little cooler. However, when it's cool, sperm don't like that either. The testicles are pulled up closer to the body to keep them warm.
Also, when your guy has an erection, he may be doing kegels. Consciously or unconsciously, the result is that his balls can be pulled up. If he doesn't have a full erection, ask him to flex his cock. You'll see his cock jump a little, but if you look closer you'll also see his balls lift slightly. If he's clenching for a long time - which happens easily if you are giving him head, his balls can pull tightly against his body, as you describe.
His balls may seem smaller simply because they aren't hanging as beautifully and are half hidden in his crotch.
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