Common Guinea Pig Health Issues (And Why Vitamin C Matters So Much)

Guinea pigs mask illness well, which means routine care matters more than it might seem to when everything looks fine. A handful of conditions come up often enough that every owner should be able to recognize them.

Upper Respiratory Infections and Pneumonia

Caused by bacteria like Bordetella bronchiseptica, Streptococcus or Staphylococcus species, and made more likely by poor husbandry, vitamin C deficiency and a young age. This one is genuinely urgent: guinea pigs are obligate nasal breathers, meaning they can't fall back on mouth-breathing the way many other animals can if their nasal passages are blocked, so a guinea pig breathing with its mouth open needs a vet immediately.

Watch for: sneezing, nasal or eye discharge, noisy or labored breathing, lethargy and a drop in appetite. All of these warrant a same-day vet visit rather than a wait-and-see approach, since pneumonia can end in sudden death. Rabbits and dogs can carry Bordetella without looking ill and pass it on to a guinea pig.

Vitamin C Deficiency (Scurvy)

Guinea pigs, like humans, can't produce their own vitamin C, which makes this a genuinely species-specific concern. Deficiency weakens the immune system, slows wound healing, and disrupts normal bone and tooth development. This is almost entirely preventable through diet, and our Guinea Pig Scurvy guide has the daily vitamin C numbers in full. A reliable vitamin C supplement is a straightforward way to close the gap if you're ever unsure your pellets are still fresh.

Dental Disease

All of a guinea pig's teeth grow throughout life, and the molars can overgrow even when the front incisors look completely normal, which is part of why this condition catches owners off guard. When an adult's incisors suddenly look overgrown, the trouble is often at the back of the mouth.

Watch for: drooling or a wet, matted chin and neck, reluctance to eat despite interest in food, trouble chewing or swallowing, weight loss, and unusually small droppings. The signs are vague, so a vet examines the back teeth with special instruments. Treatment is reducing the crowns with a dental drill under general anesthesia, and sometimes pulling a tooth. Severe or chronic cases can need the procedure repeated as often as every 4 to 6 weeks, which is part of why prevention through a proper hay-based diet matters so much. Vitamin C deficiency is another cause.

GI Stasis

Life-threatening and can develop quickly, within 24 to 48 hours if it goes untreated. A guinea pig that stops eating and is passing very little or no stool needs urgent veterinary attention, not a wait-and-see approach; our feeding guide has the exact hours-without-eating clock. A low body temperature alongside these signs makes it more urgent still.

Treatment is supportive: fluids for dehydration, assisted feeding with a critical care diet, pain relief and drugs that get the gut moving again. A vet may send you home to give food and medicine by syringe, placed into the side of the mouth and past the loose tissue behind the front teeth. With prompt care many guinea pigs improve within 24 to 72 hours, though full recovery can take several days to a week.

Bladder Stones (Urolithiasis)

Roughly 90 percent of stones identified in guinea pigs are calcium carbonate, which sets them apart from the struvite or oxalate stones common in dogs and cats. That difference matters in practice: there's no prescription diet or medication that dissolves calcium carbonate stones once they've formed. Surgical removal, a cystotomy, is generally the only way to resolve one. Small stones sometimes cause few or no symptoms at first, which is part of why waiting for obvious signs can mean a stone has already grown large enough to need surgery by the time it's caught. Males face the higher risk of a life-threatening blockage of the urethra.

Watch for: squeaking or crying out while urinating, straining or repeated attempts to urinate, a hunched posture, blood in the urine, and urine staining or matted fur around the hindquarters. Any of these is worth a same-day vet visit, since a stone can also cause a partial or complete blockage, which is a true emergency.

Diet plays a real role here, though it isn't the whole story. High-calcium foods, alfalfa hay especially, along with certain leafy greens like kale, spinach, and parsley, add to the calcium load that ends up in the urine, and low water intake concentrates that urine further, making crystal formation more likely. Adult guinea pigs generally do better on timothy hay, since alfalfa is really only appropriate for young, pregnant, or nursing guinea pigs. Increasing water intake and reducing calcium consumption are the cornerstones of managing a guinea pig prone to stones, and a water bottle tends to increase daily intake over a bowl. Neither is a guarantee, though. Medical management on its own is often unrewarding, and recurrence after surgery is common, so diet and water intake stay worth watching well after a stone has been removed.

If a secondary bladder infection is part of the picture, a vet may prescribe antibiotics, and guinea pigs tolerate only a narrow list of them safely. Penicillins such as amoxicillin, lincosamides such as clindamycin, macrolides such as erythromycin, and cephalosporins can wipe out the gut bacteria that keep a guinea pig's digestion stable and trigger fatal enterotoxemia, so ask which drug it is before the first dose.

Skin Mites, Lice and Ringworm

All of these cause hair loss, crusting or flaky skin, and each needs a vet to tell it apart and treat it.

Mange mites (Trixacarus caviae) cause intense itching, so severe that the scratching can look like a seizure. A guinea pig that suddenly thrashes or runs while scratching hard may have mites rather than a neurological problem, and the skin underneath ends up crusty, raw and prone to infection. Lice cause hair loss and crusty lesions, typically around the face, behind the ears or over the shoulders, and a vet confirms them under a microscope. Ringworm is a fungus, not a worm, and shows as circular patches of hair loss ringed by inflamed, crusted skin, most often on the face, head and ears.

Ringworm and some mite infestations are zoonotic, meaning they can spread to people in the household, so wear gloves and wash your hands when treating a guinea pig, and treat promptly rather than letting these run their course.

Ovarian Cysts

Ovarian cysts are extremely common in unspayed female guinea pigs, and the risk climbs with age, yet this is one of the most under-recognized conditions on this list because the most visible sign often gets mistaken for a skin problem rather than a reproductive one.

The differential against mites matters here. Mites cause intense itching, a guinea pig scratching hard and often, and skin that looks visibly irritated, scabbed, or raw underneath the missing fur. Ovarian cysts produce a very different picture: hair loss is symmetrical across both flanks, the skin underneath looks completely normal, and there's no itching at all. An older intact female losing hair evenly on both sides without scratching points toward cysts before mites.

Not every cyst behaves the same way. Functional cysts secrete hormones and are the ones behind the hair loss, nipple changes, and sometimes aggressive or mounting behavior in an affected female. Non-functional cysts don't secrete hormones but can still cause real discomfort simply by growing large enough to press on nearby organs.

Other signs to watch for include crusty or noticeably enlarged nipples, since these cysts are often hormonally active, a firm or visibly swollen abdomen as the cyst grows, and lethargy or a drop in appetite as it presses on nearby organs.

Diagnosis starts with abdominal palpation, where a vet may be able to feel an enlarged ovary directly, but ultrasound is the more reliable way to confirm a cyst and rule out other causes of abdominal swelling. Spaying, an ovariohysterectomy, is the definitive treatment. It resolves the cysts outright and prevents them from recurring on remaining ovarian tissue, which can happen with less complete surgical approaches. Because surgery carries more risk in an older or already-debilitated guinea pig, catching this early, before significant abdominal distension sets in, makes a real difference in how well she comes through it.

Should a Healthy Female Be Spayed?

Studies have found ovarian cysts in more than half of female guinea pigs, older sows most often, and reproductive disease is the third most common reason guinea pigs see a vet at all. That is the case for a preventive spay, and it is one exotics vets make for young, healthy sows. At that age the ovaries alone can be removed through a small incision in each flank. That is a shorter surgery than the traditional belly approach, it keeps the surgeon clear of the guinea pig's large cecum, and it lowers the risk of pain, appetite loss and GI stasis afterward. An older female that already has cysts usually needs the full ovariohysterectomy instead, because the uterus is often diseased as well. So the time to raise it with an exotics vet is while she is young and healthy, before she reaches the age when cysts are most likely and surgery carries more risk. A sow kept only with other females needs no spay for contraception, so for her the decision rests on the cyst risk alone.

Pregnancy and Pregnancy Toxemia

Pregnancy lasts 59 to 72 days, and a sow that has not delivered by day 70 needs a vet immediately. Exhaustion, persistent unproductive contractions or heavy bleeding during labor are also reasons to go straight to one. Pregnancy toxemia is the other serious risk, most likely in overweight sows or those not eating well, which is why a pregnant guinea pig that stops eating is an emergency and not a 12-hour wait.

A Few Other Conditions to Know

• Bumblefoot (pododermatitis), a painful foot infection linked to wire flooring or unsanitary bedding, and also to obesity, arthritis, overgrown nails and vitamin C deficiency. Mild cases are treated with topical care, bandages, pain relief and vitamin C while the cause is fixed, and a deep infection leaves the animal lame and in pain. Solid-floor housing with clean paper bedding goes a long way toward preventing it.
• Lumps in the neck, often an infected lymph node (cervical lymphadenitis) that follows a scrape inside the mouth. It shows as a large swelling on one side of the neck and is treated with surgery and antibiotics. Any new lump needs a vet, since abscesses, cysts and benign skin tumors all look alike from the outside.
• Boar butt, an impacted rectal pouch. Males, older intact ones especially, have a pouch behind the anus where droppings can pack in, causing smell, irritation and infection. Check older boars for it, and ask the vet to show you how to clean it; castration prevents it.
• Heat stress and heatstroke, since guinea pigs are highly heat sensitive and can overheat quickly in warm weather. The small mammal heat stress guide has the signs and the cooling steps.

Reading Droppings and Urine

Healthy droppings are small, firm, well-formed teardrop or oval pellets in dark brown, and plentiful. Fewer, smaller or no droppings means the gut is slowing, so treat it like a refusal to eat. Guinea pigs also eat some of their own droppings straight from the body, and that is normal. Diarrhea is watery, unformed or foul-smelling stool, not just a few soft droppings, and it needs a vet the same day, especially with lethargy, a loss of appetite or a recent antibiotic. Urine runs from pale to reddish-brown depending on the diet, so color alone does not mean blood; straining, crying out or a stained rear end do mean a bladder problem.

Normal Numbers to Know

Adult boars weigh 900 to 1,200 g and sows 700 to 900 g, and a healthy guinea pig breathes 40 to 100 times a minute, quietly and through the nose. Its own steady weight on a weekly gram scale is the best baseline to hand a vet.

When to See a Vet

Because guinea pigs hide illness well, an annual wellness exam matters even when your guinea pig seems completely healthy. See a vet promptly, not on a wait-and-see basis, for refusal to eat, drooling, labored or open-mouth breathing, diarrhea, lethargy, a hunched posture, straining to urinate with nothing passing, or a pregnant sow that stops eating. A cavy-savvy exotic vet is worth locating before an emergency, since general small-animal clinics aren't always equipped for guinea pig-specific issues.

The Guinea Pig encyclopedia profile covers the wild ancestry behind an animal that hides illness this well.

Sources & Further Reading

Printable Guide

A sick guinea pig is no time to be scrolling. The Guinea Pig Care Package puts these red flags, a symptom quick reference and an emergency card on paper, in a 51-page PDF, $8.99.

Read the first 5 pages free