DDx: Can you spot these summer health hazards?

Spider bite vs deer tick bite (Lyme disease)

Signs and symptoms of spider bite may include itching or rash, pain radiating from the site of the bite, reddish to purplish color or blister, fever, chills, headache, muscle pain or cramping, increased sweating, difficulty breathing, nausea and vomiting, anxiety or restlessness, or high blood pressure.

Signs and symptoms of Lyme disease from a deer tick bite include fever, chills, headache, fatigue, muscle and joint aches, and swollen lymph nodes. The characteristic erythema migrans (bull's-eye) rash does not occur in 20% to 30% of patients.

What is this summer danger? This photo shows a brown recluse spider bite. A small white blister can appear at the site of the bite, which may develop into a severe lesion (skin necrosis) due to the venom. Brown recluse spider bites are uncommon and considered to be overdiagnosed—they are typically only found in Midwestern and Southern states. (Researchers have developed a mnemonic device to avoid misdiagnosing brown recluse spider bites.)

Poison ivy vs scabies

Poison ivy is characterized by itchy skin, redness or red streaks, swelling, small or large blisters often forming streaks or lines, and crusting skin (after blisters burst).

Signs and symptoms of scabies include itching (mainly at night), rash with little bumps that often form a line, sores from scratching, and sometimes thick crusts on the skin.

What is this summer danger? This is a photo of scabies, which is caused by the bite of the human itch mite. Scabies can develop any time of year and anywhere on the body, although the most common areas are between the fingers, around nails, elbows, wrists, buttocks, belt line, penis, around the nipples, and on skin covered by a bracelet, watchband, or ring. The mites are most often transferred through direct, skin-to-skin contact.

Chickenpox vs 'hot tub rash'

Despite the development of a chickenpox (varicella zoster virus) vaccine, some children still present with the disease. The most common symptom is an itchy rash that turns into small, fluid-filled blisters and then scabs. The rash usually appears first on the face, chest, and back, and then spreads to the rest of the body. Other symptoms include fever, tiredness, loss of appetite, and headache.

Hot tub rash—also known as water slide rash and Pseudomonas folliculitis or dermatitis—appears as itchy spots on the skin that become a bumpy red rash with pus-filled blisters around hair follicles. The rash is typically worse on skin covered by a swimsuit.

What is this summer danger? Pictured here is hot tub folliculitis, a community-acquired skin infection resulting from exposure to water contaminated with Pseudomonas aeruginosa. While Pseudomonas is common in the environment, hot tub rash occurs when the water in a hot tub, pool, or water slide is poorly maintained and the skin is exposed for a prolonged period. The rash typically develops a few days after exposure. The best way to avoid it is to change out of your swimsuit after getting out of the water and shower with soap.

Heat rash vs hives

Heat rash (also called prickly heat or sweat rash) occurs frequently in hot, humid, or tropical climates. Common signs and symptoms of the most common type of heat rash (miliaria rubra) include very itchy, small (2–4 mm), red, nonfollicular papules and papulovesicles, often accompanied by background redness of the skin. In children, miliaria appears in the skin folds of the neck, axilla, or groin. In adults, it often affects the upper trunk, scalp, neck, and in skin folds that rub against clothing.

Hives are itchy (sometimes stinging or burning) slightly raised, pink or red swellings or welts. These can occur alone or in a group, or connect over a large area. The swellings often subside or resolve within 24 hours in one area of the skin, only to surface in another area.

What is this summer danger? This photo illustrates hives, which often develop as a result of allergy (as well as many other causes). Although similar in appearance to hives, heat rash is caused by blockage and/or inflammation of sweat ducts.

Swimmer's itch vs chigger bites

Signs and symptoms of swimmer's itch include an initial itchy or tingling sensation with tiny red spots on the affected skin. Within hours, the red spots enlarge into papules (and occasionally hives) that are intensely itchy. Blisters may develop in the next 24 to 48 hours.

Chigger bites are characterized by severe itching, swelling, and clusters of red papules and papulovesicles, most commonly affecting the legs and waistline. Itching generally subsides within 72 hours of the chigger bite and cutaneous lesions typically heal within 1 to 2 weeks. "Summer penile syndrome"—a triad of penile swelling, itching, and painful urination—may occur in boys who have a local hypersensitivity to chigger bites. This syndrome can last for a few days to a few weeks.

What is this summer danger? Pictured above is swimmer's itch, which is a skin rash (cercarial dermatitis) caused by an allergic reaction to an infestation of larval-stage parasitic flatworms (schistosomes) found in lakes, ponds, and lagoons. The flatworm's preferred hosts are ducks, geese, gulls, and other waterfowl, but will sometimes infect humans out swimming. The rash usually appears on areas of the body exposed directly to water, so skin under swimwear is often protected. The rash typically resolves within several weeks without treatment.

Chiggers are mites (known as harvest mites, redbugs, and other names) also in the larval stage. They're typically found in forests, grassy areas, gardens, and moist areas of soil near bodies of water. While the chigger's initial bite is painless, its feeding process in the epidermis leads to the itchy spots and swelling. As with swimmer's itch, the presentation of chigger bites resolves on its own in a few weeks, and treatment focuses on symptomatic relief.