What Are Human Parasites?

Parasites are organisms that live in or on the body and depend on it for survival. They fall into three main categories:

• Protozoa: Microscopic, single-celled organisms such as Giardia and Cryptospoidium
• Helminths: Worms, such as roundworms, tapeworms and hookworms
• Ectoparasites: Organisms that live on the skin, such as lice, ticks or mites

How Do People Get Parasites?

Parasites spread in several ways. Understanding these routes can help reduce risk. Common sources include:

• Drinking contaminated water
• Eating undercooked or raw food
• Poor hand hygiene
• Contact with infected soil
• Travel to areas where parasites are more common
• Close contact with infected people or animals

Many digestive symptoms people blame on parasites are actually caused by more common conditions, such as food intolerance, irritable bowel syndrome (IBS), viral gastroenteritis or stress.

Symptoms of Parasitic Infections

Symptoms vary by parasite type and overall health. Possible signs include:

• Stomach pain or cramps
• Ongoing diarrhea or loose stools
• Nausea or vomiting
• Fatigue
• Unexplained weight loss
• Blood or mucus in your poop
• Itching around the anus (especially in children)

These symptoms alone don’t confirm a parasite. Many conditions can cause similar issues. That’s why self-diagnosing based on symptoms alone is unreliable.

How Are Parasites Diagnosed?

If you suspect a parasite, your first step should not be a cleanse or supplement. It should be a visit to your doctor who will ask you about:

• Your symptoms and how long they’ve lasted
• Recent travel history
• Foods and water consumed
• Exposure to animals or soil
• Medications you take
• Your immune system status

If your case is complex, you may be referred to a gastroenterologist or infectious disease specialist.

Diagnostic Testing

• Stool testing: The most common test for intestinal parasites is the ova and parasite (O&P) stool test. A sample is examined under a microscope for parasites and their eggs (ova). For accuracy, you may need to collect multiple samples on different days.
• Blood testing: Blood tests can detect systemic parasites like Toxoplasma gondii or those causing filariasis.
• Tape test: For suspected pinworms, your doctor may recommend that you press clear tape, sticky side down, on the skin around the anus to collect any pinworms or eggs. Bring the tape to your doctor, who will examine it under a microscope.
• Imaging and Endoscopy: When stool tests are inconclusive, imaging (ultrasound, CT, MRI) or direct visualization through endoscopy or colonoscopy may be used to identify parasites or structural issues.

“Proper diagnosis of a parasite infection relies on targeted testing, no guesswork,” says Ihab Syed Ahmed, MD, an infectious disease specialist at Northwestern Medicine. “Stool testing remains the cornerstone for intestinal parasites, and your clinician may order multiple types of tests to ensure an accurate diagnosis and effective treatment.”

Do Parasite Cleanses Work?

The short answer is no.

Herbal cleanses and supplements marketed online:

• Lack reliable evidence
• Can cause dehydration, diarrhea, electrolyte imbalances or liver injury
• Delay proper diagnosis and treatment

Some “worms” that people see after cleanses are actually mucus or intestinal lining, not parasites.

“If an over-the-counter cleanse truly killed parasites, it would be classified and regulated as a medication, which these products are not,” says Dr. Ahmed.

Prescription Medications

If a parasite is confirmed, prescription medications are the standard and effective treatment. These medications:

• Target the specific organism
• Are usually taken for a short, defined course
• Have known safety profiles
• Are highly effective when used properly

“Different parasites require different treatments, which is why identifying the organism matters,” says Dr. Ahmed.

Can You Prevent Parasites?

Prevention focuses on basic hygiene and food safety:

• Wash hands thoroughly, especially after bathroom use and before eating
• Drink trusted or safe water
• Wash fruits and vegetables well with safe water
• Cook meat to safe temperatures
• Avoid walking barefoot in unsanitary areas
• Practice good pet hygiene and veterinary care

For most people in developed countries, these measures make parasitic infections uncommon.

“Prevention through hygiene and sanitation remains the pillar of reducing parasitic infection risk,” says Dr. Ahmed.

If You Think You Might Have a Parasite

Don’t panic, and don’t self-diagnose. Instead:

• See a healthcare professional.
• Get proper testing.
• Follow evidence-based treatment if a parasite is found.