Guinea pigs very rarely bite. When they are frightened, they prefer to run and hide, instead of fighting, so children and adults can safely handle them without fear. Still it is always a good idea when handling any small pet to wash your hands thoroughly before you pick them up, especially if you have been dealing with food. If your fingers smell like food, then the guinea pigs may mistakenly be biting you.
Baby guinea pigs do have a tendency to nibble on fingers because, just like any young animal, they learn about their environment by exploring it with their mouths. Eventually, they will outgrow this.
On occasion you may find a guinea pig that does bite. This is relatively rare, but it does happen sometimes. When it does, you don't need to give up on the guinea pig, he can be helped.
Usually, there are two reasons why an animal bites:
1. They are afraid of you
OR
2. They feel they are more dominate than you.
Before you help your guinea pig with its problem, you need to determine which of these is the case for your pet.
A guinea pig who bites out of fear is usually very timid and may try to avoid you, even in the cage. He may curl up into the corners so that you can't find him. When you touch him, the guinea pig may start shivering or shaking because he is afraid. In these cases, the guinea pig is so scared that he feels he has to fight back in order to defend himself. To stop this behavior, you must start slowly.
Don't pick up the animal, but instead start by reaching into the cage and stroking its head briefly. Then, gradually increase your contact with the guinea pig until it feels comfortable with you handling him. It may take awhile and it may require a great deal of patience, but the payoff will be a closer relationship between the two of you and a happier guinea pig.
There are also two ways you don't want to handle either of these situations. First, never make sounds like an injured guinea pig if he bites you. Some people foolishly believe that the guinea pig will feel so bad for causing you pain that he'll immediately stop, but that's not how the animal thinks. Instead, they feel more dominate since a whining guinea pig is usually the weaker one, and your problems will only get worse. Another thing not to do is to yell or hit your guinea pig.
Because biting is a rare possibility, it is usually better for an adult to handle the animal for the first few days to make sure that this type of behavior isn't going to be a problem.