Giardia-infected stool is typically pale, greasy, and soft, with a distinctly foul smell often compared to rotten eggs. It tends to float in the toilet bowl because of its high fat content, and it may appear lighter in color than normal, ranging from yellow to tan. There is no blood or pus in giardia stool, which is one of the clearest ways to distinguish it from bacterial infections.
Why Giardia Stool Looks Greasy and Floats
The Giardia parasite attaches to the lining of your small intestine and interferes with how your body absorbs fat. It does this partly by disrupting bile salts, the compounds your digestive system uses to break down dietary fat. When fat passes through unabsorbed, it ends up in your stool, creating a condition called steatorrhea. About 27% of giardia patients in one study had measurable fat malabsorption.
This excess fat is what gives giardia stool its distinctive greasy, oily appearance. It also makes the stool lighter in color and buoyant enough to float. You might notice it leaves a slick or residue in the toilet bowl that’s harder to flush than normal stool. The texture is typically soft to mushy rather than fully liquid, though watery diarrhea can also occur.
The Smell Is Distinctive
Giardia stool has a sulfurous, egg-like odor that most people describe as significantly worse than ordinary diarrhea. The smell comes from the malabsorbed fat combined with excessive gas production in the gut. You’ll likely notice foul-smelling burps as well, along with bloating and frequent flatulence. These sulfurous burps are actually one of the more recognizable early signs of giardia infection and can appear before stool changes become obvious.
What Giardia Stool Does Not Look Like
One of the most useful things to know is what giardia stool will not contain. There should be no blood, no visible mucus streaks, and no pus. If you see blood in your stool alongside diarrhea, that points toward a bacterial infection like Salmonella, Shigella, or Campylobacter, or possibly an inflammatory bowel condition. Giardia is a surface-dwelling parasite that doesn’t invade the intestinal wall, so it doesn’t cause the tissue damage that produces bloody stool.
Compared to another common waterborne parasite, Cryptosporidium, giardia stool tends to be greasier and more foul-smelling. Cryptosporidium diarrhea is usually more watery and voluminous without the same oily quality, because it primarily causes fluid loss rather than fat malabsorption.
Timeline: When Stool Changes Start and How Long They Last
Symptoms typically begin 1 to 14 days after swallowing the parasite, with an average of about 7 days. During the first week of illness, you may notice your stool becoming progressively softer, paler, and more foul-smelling. The acute phase usually lasts 1 to 3 weeks, but some people develop chronic symptoms that persist for months without treatment.
Even after treatment clears the parasite, your stool may not return to normal immediately. The intestinal lining needs time to repair itself, and this recovery can take several months. During that period, you may experience temporary lactose intolerance, meaning dairy products could trigger loose stools and bloating even though the infection is gone. This is normal and resolves as the gut heals.
Giardia Stool in Dogs and Cats
If you’re checking your pet’s stool, the signs overlap with humans but aren’t always dramatic. In dogs, the most common change is a pungent odor (seen in about 36% of infected dogs), followed by mushy consistency (28%) and soft stool (24%). Cats show a slightly different pattern: soft stool is the most frequent sign (38%), followed by mushy stool (26%) and pungent odor (20%).
Notably, about 25% of both dogs and cats with confirmed giardia infections show no visible stool changes at all. Their poop looks and smells normal despite actively shedding the parasite. This is why veterinarians recommend testing rather than relying on appearance alone. When changes do appear in pets, you’re looking for the same general pattern as in humans: soft or mushy (not necessarily liquid), lighter in color, and unusually smelly. Frank diarrhea occurs in fewer than 5% of infected pets.
Getting a Diagnosis From a Stool Sample
If your stool matches this description, especially the combination of greasy, floating, foul-smelling, and bloodless, a stool antigen test is the most reliable way to confirm giardia. These tests detect proteins from the parasite directly in your stool sample and have a pooled sensitivity of about 92% and specificity of 97%, making them significantly more accurate than the older method of looking for parasites under a microscope. The antigen-based approach catches roughly 30% more infections than microscopy alone.
Your doctor may ask for a single stool sample, though giardia can shed intermittently, so a negative result doesn’t always rule it out. If your symptoms strongly suggest giardia but the first test is negative, a repeat sample collected on a different day improves the chances of detection.