It is true that varicocoeles (which are really like varicose veins of the scrotum) can increase the temperature of the scrotum and therefore have a detrimental effect on the way the testicles work, but the effect is very variable. Varicocoeles can be tied off by a small operation and this can improve the number of sperm that are produced, but there is very little proof that this increases fertility. The damage appears to occur at the time of puberty and may be partly irreversible.