Acariasis is any infestation of the body by mites, tiny arthropods related to spiders and ticks. While the term most commonly refers to skin infestations like scabies, mites can also colonize the lungs, intestines, ears, and urinary tract. An estimated 200 million people worldwide are affected by scabies alone, making it the most widespread form of acariasis and a significant global health concern.
Types of Acariasis
Most forms of acariasis are external, meaning the mites live on or within the skin. Scabies is the best-known example. Other mites colonize hair follicles or live on the skin’s surface, causing inflammation and irritation. Some forms are passed between animals and humans, particularly from dogs, cats, and livestock carrying their own species of mites.
Less commonly, mites can infest internal tissues. Pulmonary acariasis involves mites in the airways and lungs. Intestinal, oral, urinary, and even vaginal acariasis have all been documented, though these internal forms are far less understood. Certain mite species also inhabit the respiratory tracts of birds and mammals, or burrow into deeper tissues like fat and muscle during parts of their life cycle.
Domestic mites, the same species known for triggering allergies, are also responsible for non-allergic symptoms when they invade and parasitize human tissues. This means the line between “harmless allergen source” and “active parasite” is blurrier than most people realize.
How Mites Damage the Body
In scabies, the most studied form of acariasis, female mites burrow into the outermost layer of skin using specialized cutting mouthparts and hooks on their legs. They dig tunnels where they move, feed, deposit waste, and lay eggs. To make burrowing easier, the mites release substances that break down surrounding skin tissue.
The damage you feel isn’t mostly from the burrowing itself. It’s from your immune system reacting to the mite’s waste products, saliva, and eggs deposited under the skin. Two types of immune response kick in: an immediate allergic reaction (similar to hives) and a slower, delayed inflammatory response that builds over days to weeks. This is why itching from a first-time scabies infestation often doesn’t start until several weeks after the mites arrive. Your body needs time to develop sensitivity to the foreign material. On re-infestation, symptoms can appear within hours because your immune system already recognizes the threat.
Symptoms and Where They Appear
Intense itching, especially at night, is the hallmark of skin-based acariasis. The itch is relentless and tends to worsen in bed because mites are more active in warmth. Common sites include the spaces between fingers, the wrists, elbows, armpits, waistline, buttocks, and genitals. In infants and young children, the palms, soles, face, and scalp can also be involved.
Visible signs include thin, irregular burrow tracks (often grayish or skin-colored lines a few millimeters long), small red bumps, and sometimes fluid-filled blisters. Persistent scratching frequently leads to open sores, crusting, and thickened skin. In severe cases known as crusted (or Norwegian) scabies, thick layers of skin harbor thousands to millions of mites, compared to the 10 to 15 mites typically present in ordinary scabies. Crusted scabies is most common in people with weakened immune systems or reduced sensation.
For internal forms of acariasis, symptoms depend on the location. Pulmonary acariasis can cause chronic cough and wheezing. Intestinal acariasis may produce abdominal discomfort. These internal presentations are often misdiagnosed because clinicians don’t routinely consider mites as a cause of respiratory or gastrointestinal symptoms.
How Acariasis Spreads
Scabies spreads through prolonged, direct skin-to-skin contact. Brief handshakes or hugs rarely transmit mites. Sexual contact, sharing a bed, and caregiving activities (bathing, dressing) are the most common routes. In crusted scabies, the massive number of mites makes transmission much easier, even through brief contact or shared surfaces.
Mites can survive off a human host for 24 to 36 hours at normal room temperature and moderate humidity. In cooler, more humid conditions, survival extends significantly: mites have been documented living up to 19 days at 10°C with very high humidity, though they can’t move well or penetrate skin below 20°C. At warmer temperatures around 34°C, they die within 24 hours. This survival window explains why contaminated bedding, clothing, and towels can be a secondary source of infestation, particularly in institutional settings like nursing homes.
Diagnosis
The traditional method for confirming scabies is a skin scraping examined under a microscope. A clinician scrapes a suspected burrow with a blade, places the sample on a slide, and looks for mites, eggs, or fecal pellets. This approach is highly specific (if you find a mite, you have your answer) but only catches about 50% of cases, because the number of mites on the skin is often very low.
Dermoscopy, which uses a handheld magnifying device to examine the skin surface, is another option, but its accuracy depends heavily on the examiner’s experience. More recently, PCR-based tests that detect mite DNA from skin scrapings have shown higher sensitivity than microscopy. These molecular tests can identify cases that microscopy misses, making them particularly useful for suspected scabies that hasn’t been confirmed by traditional methods.
In practice, many cases are diagnosed clinically based on the combination of typical itching, characteristic lesion distribution, and a history of close contact with someone who has scabies. International consensus criteria classify cases as confirmed (mites seen under microscopy), clinical (typical features with supporting history), or suspected (some but not all typical features).
Treatment
For ordinary scabies, the standard topical treatment is a 5% permethrin cream applied to the entire body from the neck down and washed off after 8 to 14 hours. A single application is often effective, but two treatments spaced about a week apart are commonly recommended to catch any mites that hatch from eggs after the first application.
An oral anti-parasitic medication is the main alternative, taken as a single weight-based dose. A second dose one week later reduces the risk of treatment failure. This oral option is especially useful for large outbreaks or when applying cream to the entire body is impractical.
Crusted scabies requires a more aggressive approach: topical cream applied to the entire body (including the head) combined with oral medication. The thick, crusted skin needs to be softened and removed with keratolytic agents so the topical treatment can actually reach the mites. Multiple rounds of treatment over one to two weeks are typical.
Itching commonly persists for two to four weeks after successful treatment. This doesn’t mean the treatment failed. It reflects the ongoing immune reaction to mite debris still present in the skin, even after the mites themselves are dead.
Preventing Reinfestation
Treating the infested person alone isn’t enough. All household members and close contacts should be treated simultaneously, even if they aren’t itching yet, because the weeks-long delay before symptoms appear means they may already be carrying mites.
Bedding, clothing, towels, and any fabric that touched the skin in the days before treatment should be machine-washed in hot water above 75°C, then run through a hot dryer cycle. Items that can’t be washed can be sealed in a plastic bag for at least 72 hours, since mites die within a day or two without a host at room temperature. In institutional settings like care facilities, coordinated treatment of all residents and staff is critical to breaking the cycle of transmission.
Global Burden
Scabies affects roughly 200 million people at any given time, with the highest burden in tropical regions of Asia, Oceania, and Latin America. A large meta-analysis found a pooled global prevalence of about 12%, though rates vary enormously by region and population. Overcrowded living conditions, limited access to treatment, and poverty all drive higher rates. In 2017, the World Health Organization added scabies to its list of neglected tropical diseases, recognizing it as a public health priority rather than a minor nuisance.
Secondary bacterial infections are a major concern in high-burden areas. Persistent scratching breaks the skin barrier, allowing bacteria to enter. These infections can lead to abscesses, and in some populations, post-infectious complications affecting the kidneys and heart. The harm from acariasis extends well beyond the itch.