How Is Scabies Diagnosed?

Scabies is a contagious, itchy skin rash caused by tiny human itch mites (Sarcoptes scabiei) that burrow into the top layer of skin to feed and lay eggs, which causes an intensely itchy rash. Scabies spread through prolonged skin-to-skin contact, such as holding hands or sharing bedding or clothing with someone who has scabies.

Primary care providers (e.g., pediatricians, general practitioners) and dermatologists (doctors who specialize in the skin, hair, and nails) can diagnose scabies. Scabies is diagnosed by examining the skin to look for the characteristic pimple-like rash and burrows (tunnels) the mites make as they lay eggs just under the skin’s surface. Lab tests can help rule out other conditions that cause similar symptoms and confirm a scabies diagnosis.

Diagnostic Criteria

The International Alliance for the Control of Scabies (IACS) Consensus Criteria for the Diagnosis of Scabies is the diagnostic criteria developed by an international group of researchers, clinicians, and public health experts. The criteria categorizes the diagnosis of scabies at three levels:

• Confirmed scabies: Requires direct visualization of the mites or their eggs or feces using a dermatoscope (a handheld device similar to a magnifying glass). 
• Clinical scabies: Relies on the clinical assessment of signs and symptoms, such as a rash, burrows, and intense itching.
• Suspected scabies: When a person has itching or previous contact with someone with scabies, but visible signs are absent or do not look like a typical scabies rash. 

The IACS criteria recommend healthcare providers assess the following to make a scabies diagnosis:

• Signs and symptoms: A pimple-like rash, burrows, and intense itching that worsens at night.
• Distribution of lesion: A rash and burrows in areas of the body where scabies is typically found, including the palms of the hands, soles of the feet, between fingers and toes, armpits, chest, groin, genitals, wrists, and waist.
• History of exposure: Having a history of close contact with someone with scabies.
• Laboratory testing: Microscopic examination of skin scrapings confirms the diagnosis of scabies.

Medical History

When you visit a healthcare provider for a possible scabies diagnosis, they will begin by asking about your symptoms and medical history. Evaluating your symptoms and history can help reveal important information about whether you have or are at risk of scabies. Your healthcare provider may ask:

• Whether you’ve had close contact with a person with scabies 
• If you’ve recently traveled to an area where scabies is more common 
• Whether you have intense itching that worsens at night or a pimple-like rash
• If you have skin conditions, allergies, or chronic illnesses that may affect your skin’s appearance or health 
  

Physical Exam 

Your healthcare provider will examine your skin to look for the classic signs of scabies, including a red, pimple-like rash and burrows on the skin. Scabies burrows are small, thread-like lines commonly found in areas of the body with skin folds, such as the webbing between fingers, toes, and the wrist. 

They may use a dermatoscope—a handheld device that uses magnification and illumination (light) to examine the skin closely. It can help healthcare providers see mites, eggs, or feces not visible to the naked eye.

Skin Scraping 

Skin scraping is a procedure that can confirm the presence of scabies mites beneath the skin's surface. This test helps rule out other conditions with similar symptoms. Using a scalpel or tip of a needle, healthcare providers scrape a small amount of skin from the area where a suspected scabies rash is present. The collected sample is examined under a microscope to check for scabies mites, eggs, or fecal matter to confirm a scabies diagnosis.

Skin scraping test results are not always accurate, so your healthcare provider may also recommend other tests, such as an ink test, to provide an accurate diagnosis.

Ink Test

A burrow ink test is a simple, non-invasive test that can help diagnose scabies. Ink from a fountain pen or marker is rubbed onto the affected skin area. Excess ink is wiped off. If burrows are present, the ink will sink into them and appear as thin, wavy, ink-filled lines. This shows where a female mite has created a burrow under the skin's surface to lay eggs.

Screening for Related Conditions 

Many skin conditions can cause an itchy rash that looks similar to scabies, including:

• Atopic dermatitis (eczema): A chronic skin condition that causes itchy, inflamed, and dry skin. 
• Contact dermatitis: An itchy rash that occurs when the skin comes into contact with an allergen or irritant. 
• Papular urticaria (hives): An intensely itchy rash that causes red bumps (hives) that come and go over a month or longer. 
• Psoriasis: A chronic inflammatory skin condition that causes the rapid buildup of skin cells, leading to thick, itchy, flaky patches of skin. 
• Insect bites: Bites from mosquitoes, fleas, bed bugs, or other insects can cause itching and a rash.

A Quick Review

Scabies is an itchy, contagious rash caused by an infestation of tiny human itch mites called Sarcoptes scabiei. The mites burrow into the top layer of the skin to feed and lay eggs, leading to an intensely itchy, pimple-like rash. Healthcare providers diagnose scabies based on a thorough evaluation of your symptoms and medical history and a skin examination to look for the classic signs of scabies. They may use a dermatoscope—a tool that acts as a magnifying glass to help see mites, eggs, and feces that are not visible to the naked eye.

Diagnostic tests, such as a skin scraping or burrow ink test, can help rule out other conditions that cause similar symptoms and confirm a scabies diagnosis. Scabies is highly contagious, but it is treatable. See a healthcare provider if you suspect you have scabies or have been in close contact with a person with scabies. Treatment can help clear the infestation and prevent scabies from spreading to other body areas and people.