This article is about hairless guinea pigs, not underweight swine.
Skinny pigs are nearly hairless guinea pigs, they are most often kept as pets by people who are allergic to regular guinea pigs, or those just looking for an exotic novelty pet. There is also the baldwin guinea pig, which is truly hairless. Skinny pigs and baldwins have special care needs beyond those of a regular guinea pig.
The biggest care concern of having a skinny pig, or hairless guinea pig, is that they can get cold easily. This is not only because they lack hair to keep them warm but because of their smaller size. It is imperative their cage be kept in a warm part of the house. A cage on the floor, especially if it is tile floor, cement floor, or even a hardwood floor (unless it is a heated floor) will be cold. It can be better to put the cage on a raised table, even a table that is above, or near, a heat vent.
The cage must be kept out of any drafts, which means it should not be near a door, or window.
Many people turn down the heat in their house at night, and this can be too cold for your pet. You may find that covering the cage with a blanket helps keep the air in the cage warmer. As guinea pigs sleep at night anyhow this is usually not a problem, just make sure you remove the blanket every morning.
Another concern with skinny pigs is their skin. Without hair to draw the grease and oils off of their skin they tend to have skin problems related to the build of of these oils on their body. It is not a good idea to bathe small pets, but you can wipe a skinny pig, or baldwin, with a damp cloth once a week to remove these excess oils, especially from skin folds.
Guinea pigs can be trained to walk on a harness, but skinny pigs should only be out on a warm day, however they are very much at risk for sun burns, so should be kept in the shade and not outside for too long.
Another concern is that the metabolism of skinny pigs, and baldwin guinea pigs, requires they eat more food. On average they may need 25% more food than a regular, fully haired, guinea pig. This is not due to a health problem but simply their need for extra calories to keep warm in general.
Overall a skinny pig, or baldwin guinea pig can be a good pet for the right person. They are not suitable for people who like to keep their house cool with low temperatures.
One reason why people like these hairless guinea pigs so much is because well socialized skinny pigs and baldwins are extra cuddly, once they know your body is warm they really enjoy being held and patted.