Article: Abscesses under the skin are very common in guinea pigs. They are the body's attempt to 'wall off' an infection and keep it from spreading. Abscesses can form either after a bite from another guinea pig, or if something rough and sharp (e.g., straw) goes through the skin. They can form anywhere on a guinea pig's body, but the most common locations are the head and neck. An abscess in the neck could be a swelling of the lymph node in that area. Lymph nodes are small glands that help the body fight infection. An abscess can feel firm or soft. Abscesses can also form in the mouth or jaw of a guinea pig. Abscesses in these areas can become large very quickly. Your guinea pig may look fine on one day, then have a large abscess the next day. When you handle your guinea pig, gently open its mouth to see the abscess. If the abscess is in the jaw, you will see a large bump along your guinea pig's jawline. Guinea pigs can get several types of cysts, with the most common being a sebaceous cyst. Sebaceous cysts contain oil from the skin glands that produce oil (sebaceous glands). Sebaceous cysts are typically located on a guinea pig's back and near the rump, but can form in other places as well. Although they can become very large, cysts are usually about the size of a pea. Cysts become a problem if they become large. Tumors can also form lumps. For example, a lump on your guinea pig's tail could indicate a skin tumor called trichofolliculoma. A lump on the chest could indicate another type of cancer called lymphosarcoma. A female guinea pig can develop a mammary tumor, which you would see as a lump on the belly. Lipomas are tumors made up of fat cells. There are no specific places where you would look for a lipoma on your guinea pig. Your guinea pig may have several lipomas at one time. Sometimes, a lump can make a guinea pig feel so bad that it doesn't want to eat. For example, if your guinea pig is not eating its meals and doesn't want any tasty treats, check its mouth for an abscess. Even if your guinea pig wants to eat, the size of the abscess in its mouth or jaw could make it difficult to chew food. Sometimes, a guinea pig will stop eating right before an abscess ruptures (an abscess can sometimes rupture on its own). When you hold your guinea pig, take a quick sniff of its breath. If your guinea pig has a mouth abscess, its breath will probably smell quite unpleasant. The unpleasant smell would be due to infection. Along with bad breath, you may also notice drooling. An abscess can be very uncomfortable for a guinea pig. If your guinea pig squeals with pain when you pick it up, seems really tired, or doesn't want to play with you, it could have an abscess. You may also notice your guinea pig heavily grooming the area of the abscess.

What is a summary?
Look for abscesses on the head and neck. Identify abscesses in your guinea pig's mouth and jaw. Examine your guinea pig's back for cysts. Check for tumors on the tail and chest. Detect a decreased appetite. Smell your guinea pig's breath. Observe changes in behavior.