Sexing your hamster is only necessary if you are breeding your hamsters or you have more than one hamster and you wish to prevent breeding. No significant difference has been found in sexes as far as temperament or the ability to be a good pet, so if you are choosing a hamster that will be a solitary pet, do not worry about if your hamster is male or female. Both sexes can make loving, even-tempered and tame pets. (While there are a few owners who believe that there is a difference between the sexes, but too many exceptions can be found to substantiate these assertions).
There are both differences in body type (secondary sex characteristics) and in genitalia (primary sex characteristics) between males and females. Female adult Syrians are heavier than the males. Adult male dwarf hamsters are usually larger (slightly) than females. Male hamsters do tend to scent mark their territory more than females do, but humans do not usually detect this scent.
Males hamsters have other differences from females. For example, in males there is a longer space between their anal opening and their genital papilla. The difference in males is significant, but in females the two are very close. Adult male’s scrotum will bulge near his rump (but this is much more difficult to detect in younger males).
Females have 2 rows of 4 nipples, but these can be very difficult to see, especially in young hamsters. (You can see the nipples more easily if you gently blow on the hamster’s belly in order to part the fur – this can make the nipples more visible).
One of the easiest ways to determine the sex of a hamster is to compare it to others in the same housing area. Being able to compare body type and size, along with comparing genitalia, can make the job of sexing your hamster much easier.
Keeping males and females apart can have many benefits. Of course, unwanted litters can be avoided by keeping males and females separate. It can also help prevent the mistreatment of males Syrians by the females. The larger, heavier female Syrian hamster can be quite abusive to the male when she is not in heat and ready to mate. In extreme cases, the female can prevent the male from eating and this can eventually lead to the poor male starving to death or dying from a stress-induced disease. Keeping Syrian hamsters together in same-sex housing will reduce the risk of abuse or injury, but Syrians are not very social and should ideally be housed in solitary conditions. Sometimes, however, this is not possible due to limitations on space.
Younger male and female hamsters more difficult to tell apart. If you are not sure, consult your veterinarian or a local breeder. If you are purchasing a hamster and specifically having a male or female is important, be sure to ask the breeder or store employee to select a hamster of the appropriate sex.