Chiggers are the parasitic larval stage of mites, tiny arachnids nearly invisible to the naked eye. These larvae cause intensely itchy red welts after outdoor exposure. While a true, fluid-filled blister (vesicle) is not the typical reaction, it is possible. The inflammatory response caused by the mite’s feeding process produces large, raised papules often mistaken for blisters. In some cases, actual vesicles or pustules can form due to the host’s immune reaction or secondary infection.
The Appearance of Chigger Bites
Chigger bites generally do not cause immediate symptoms; the itching usually begins several hours after the mite has attached and started feeding. The characteristic lesions are initially small, bright red dots that rapidly develop into raised, hard papules. These bumps are often found in clusters where clothing fits tightly against the skin, such as around the ankles, waistline, and behind the knees.
The intense, localized itching is the most prominent symptom and can last for several days, sometimes persisting for up to two weeks. In some individuals, the body’s inflammatory response can cause the papules to become swollen or develop a clear fluid-filled top (a vesicle), which resembles a blister. Scratching the itchy bumps can break the skin, introducing bacteria that lead to secondary infections, resulting in pus-filled lesions or pustules that mimic blistering.
How Chiggers Cause Skin Reactions
The reaction is caused by the larval stage of the mite, the only stage that feeds on humans or animals. Contrary to misconception, chiggers do not burrow into the skin to feed. Instead, the mite attaches to the skin surface and uses its mouthparts to pierce the tissue.
Once attached, the larva injects saliva containing digestive enzymes that liquefy the host’s skin cells. The surrounding tissue reacts defensively by hardening, creating a rigid feeding tube called a stylostome. The chigger uses this structure to ingest the dissolved tissue, which provides the protein needed to develop into a non-parasitic nymph and adult.
The irritation and itching are not caused by the chigger’s presence—as the mite often detaches or is scratched off within 48 hours—but by the remaining stylostome and the host’s allergic response to the injected enzymes. The inflammation and localized swelling continue until the body can break down and absorb the stylostome tissue.
Treating the Itch and Promoting Healing
The first action after suspected exposure is to immediately wash the affected area and the entire body with soap and water to remove any attached chiggers. Using cool water and gently scrubbing the skin helps dislodge the larvae before they can feed further. Once clean, the focus shifts to managing the itching and reducing inflammation.
Over-the-counter topical treatments such as calamine lotion or anti-itch creams containing hydrocortisone can be applied to soothe the irritated skin. Taking an oral antihistamine also helps reduce the body’s generalized inflammatory response, lessening the severity of the itching. It is important to resist scratching the lesions, as breaking the skin increases the risk of a bacterial infection, which can complicate healing and lead to the formation of pustules or crusting.
Steps for Avoiding Chigger Bites
Avoiding areas known to harbor chiggers, such as tall grass, weeds, and dense brush, is the most effective preventative strategy, especially during warmer months when the larvae are active. When outdoors, wearing protective clothing provides a physical barrier against the mites. This includes long-sleeved shirts and long pants, with pant legs tucked into socks or boots to prevent access to the skin.
Applying insect repellent to exposed skin and clothing offers protection. Repellents containing DEET should be used on the skin, while products containing permethrin are effective when applied to clothing and gear, but should not be applied directly to the skin. After returning indoors, showering and washing all exposed clothing in hot, soapy water helps ensure that any clinging chiggers are removed before they can attach and begin feeding.