Originally Posted by CanadianCheese
Also, does masturbation decrease erections?
After orgasm and ejaculation, either from masturbation or any other sexual activity, there is a period, called the refractory period, during which you are unlikely to get hard again and don't have much interest in anything sexual. This can be a few hours in older men but in a teen may only be a few minutes.
It does seem that horniness gradually comes back after that, i.e. the longer it has been (within reason, from minutes up to a few days) the more easily aroused you are. That is why, if you are really horny and finding it hard to concentrate it can help to masturbate and then use this refractory period to get absorbed in whatever it is you need to concentrate on.