While most small animals don't require much grooming, guinea pigs are different. Their teeth, hair, and nails all require some specific attention on a regular basis. A guinea pig's front teeth continue to grow throughout their entire life. If they are allowed to grow without any control, the guinea pig will find it painful to eat and will, therefore, stop eating altogether.
The best thing you can do is to provide your guinea pig with hard things to chew on: carrots and other hard vegetables, chew sticks or blocks, or even tree branches. Even though you provide these materials, however, you will need to regularly check the guinea pig's teeth to make sure they aren't becoming unmanageable. Check to see if the teeth are turning inward because this is a sign of excessive growth.
If you do notice that your guinea pig's teeth are getting too long, then you need to take him to a vet and get them trimmed down. Never try to trim a guinea pig's teeth yourself! Your vet will have the proper tools and experience to safely trim the teeth to a normal length.
Another problem that sometimes arises with guinea pig's teeth, particularly if they aren't getting all of the vitamins they need in their diet, is that the tips of teeth may break off. This can also make it difficult for the guinea pig to eat. Take the cavy to your vet and feed him a softer diet until the tooth grows back properly.
Guinea pigs' hair also needs to be taken care of regularly. Keep in mind that guinea pigs with longer hair are going to require more grooming than short-haired cavies.
For short-haired guinea pigs, you need to purchase a small brush and then use it on their hair at least once a week. The brushing serves several purposes. For one, it prevents their hair from matting up and tangling. It also removes any chunks of dirt that may become mixed up in the hair. Because their hair is short, you probably will never need to trim or cut it.
Long-haired guinea pigs are a different story. They need to be thoroughly brushed at least once per day every day. If you need to go out of town for even a couple of days, You will need to leave your long-haired guinea pig with someone who can brush it for you since it doesn't take long for the hair to get terribly matted. In fact, even brushing it once per day won't be enough to stop all the tangles from forming.
You will also need to do something with the hair when it gets too long since it grows another inch in length every month. If you plan on showing the guinea pig, You will need to wrap up the extra hair so that it doesn't get caught up around the animal's feet or mixed up in the urine and feces. Special wraps are available, but You will need to contact a breeder or guinea pig club to find out where to purchase them. If you don't plan on showing your guinea pigs, You will need to trim your guinea pig's hair every couple of months. Don't cut the hair too short. You want it just short enough so that it won't interfere with your guinea pig's movement.
Regardless of the type of guinea pig you have, You will also want to do periodic inspections of its coat to check for lice. Lice are small white parasites that look like tiny worms. Guinea pigs often contract lice from hay and from other guinea pigs. If you do see lice on your guinea pig, you don't have to be alarmed. Generally, the parasites will stay on the guinea pigs and will not jump onto your children or into your home. However, the lice do need to be treated promptly. Your vet should provide you with a shampoo that will kill the lice. Shampoo your guinea pigs and thoroughly clean their cages, then repeat seven days later. You must repeat the process because it takes a week for lice eggs to hatch and you want to make sure to kill any of those remaining babies.
Finally, your guinea pig's nails need to be trimmed regularly also. While wild guinea pigs' nails are naturally worn down to an appropriate length, this does not occur in caged guinea pigs. Lengthy nails can be painful to the guinea pig and to the people who handle him, plus they can break off or get snagged which can cause further injury to your cavy.
You should allow your vet or professional guinea pig groomer to show you how to clip their nails the first time because it is more complicated than trimming your fingernails. Like most animals, guinea pigs don't like to be restrained. It makes them feel vulnerable, and they'll resist as much as they can which makes trimming their nails difficult. Your vet will be able to show you ways to restrain the animal so you safely complete the trimming.
More importantly, the guinea pig's nails contain blood vessels much like a dog's. If you trim too short, You will cut into one of those vessels and your guinea pig will bleed profusely. When this happens you must stop the bleeding immediately! It won't take long for your small pet to bleed to death if you do nothing. Many pet stores sell a powder that stops the bleeding quickly. You may want to ask your vet what he recommends.
If you're worried about cutting your pet's toenails too short, you may be better off trimming them just a little bit but more frequently.
Except for brushing the guinea pig's hair, all other parts of the grooming process should be done by an adult, not a child. Clipping nails, trimming hair, and inspecting teeth should never be done by a child. The guinea pig could become nervous and could bite out of fear for their own safety. Or the child could make a mistake that could cause pain or injury to the guinea pig.