Caterpillar rash: Symptoms and treatment

Out of curiosity or due to your love for nature, you may want to see caterpillars transform into butterflies or moths. Watch them from a distance, as the fuzzy, worm-like insects may leave you with a skin rash. You can get a caterpillar rash just by touching the insect. The hair of the insect can pierce the skin and release irritants, toxins, or allergens that trigger a reaction. The rash may last for a few days, but you may want to do something about the skin irritation, redness, and pain. There are over-the-counter ointments and oatmeal that can provide relief. You can explore more ways to treat it.

What is a caterpillar rash?

A Caterpillar rash, also known as lepidopterism, is a skin irritation or allergic reaction caused by contact with the tiny hair or spines of certain caterpillars. “The microscopic hair may contain irritating or toxic substances that trigger an inflammatory response upon contact with the skin,” says aesthetic physician and cosmetologist Dr Karuna Malhotra.

It is not contagious, as it is not caused by a pathogen like bacteria or viruses. It only develops when a person directly touches the caterpillar, its hair, or objects contaminated with them. “However, indirect exposure, such as coming into contact with clothes or surfaces with the caterpillars hair, can also cause the rash,” says the expert.

There are many caterpillars in the world that contain hair that secrete a toxin, and irritate human beings upon contact, as per research published in StatPearls in January 2024. During a 2010 study published in the Journal Of Inflammation Research, the oak and pine processionary caterpillars were found to be common causes of a caterpillar rash.

How long does a caterpillar rash last?

The duration of the rash varies, but most cases resolve within a few days to a week with appropriate care. If untreated or in cases of severe irritation, the rash might last longer, and embedded hair may prolong symptoms. Timely treatment and avoiding further exposure can significantly shorten the healing time.

What are the symptoms of a caterpillar rash?

Some of the common symptoms of caterpillar rash include:

1. Redness and inflammation

The affected skin may become red and quite swollen shortly after contact with the caterpillar hair. “This is often the body’s immediate reaction to the irritants or allergens released by the spines. In some cases, the redness may spread beyond the initial contact area,” says Dr Malhotra.

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2. Itching or burning sensation

Itchy skin or a burning feeling is one of the most common symptoms of a caterpillar rash. This can range from mild discomfort to severe irritation, depending on the caterpillar species and the person’s skin sensitivity. Scratching the area can worsen the symptoms of a caterpillar rash and increase the risk of infection.

3. Small bumps or hives

A caterpillar rash often appears as small raised bumps that look like hives or insect bites. “These may cluster together in the area of contact with caterpillar and can sometimes ooze or develop into blisters if the reaction is severe,” says the expert.

4. Pain or tenderness

Some people with a caterpillar rash experience localised pain or tenderness in the affected area, especially if the insect’s spines pierce the skin. “The pain may feel sharp, and can last for just a few hours or even days,” says the expert.

In severe cases, exposure to certain venomous caterpillars such as saddleback caterpillar, and puss caterpillar, can cause symptoms beyond the skin. “You may experience dizziness, headache, get nauseous, and have a high fever. These signs require immediate medical attention, as they may indicate a systemic allergic reaction,” says the expert.

How to diagnose a caterpillar rash?

Diagnosis of a caterpillar rash is primarily clinical and based on:

• Clinical history: The diagnosis will begin with understanding your recent activities and exposure history. A doctor may ask if you were in areas with caterpillars, such as gardens, or outdoor spaces. Details about the onset of symptoms after exposure are also crucial for identifying the cause of the rash.
• Physical examination: A close inspection of the affected skin helps identify typical signs, such as redness, bumps, and embedded hair or spines. A magnifying glass or dermatoscope may be used to detect tiny hair that are difficult to see with the naked eye.
• Ruling out other conditions: Since a caterpillar rash can resemble other skin conditions like hives, insect bites, or allergic reactions, it is important to differentiate between them. The presence of embedded hair or a specific exposure history often confirms the diagnosis.

Treatment of caterpillar rash

1. Wash the area

Remove any caterpillar hair or residue by washing the affected skin with lukewarm water and soap that will be gentle on your skin. “Avoid scrubbing or rubbing aggressively, as it can push the caterpillar’s hair deeper into the skin and worsen irritation. Washing immediately after exposure can help minimise the severity of the reaction,” says Dr Malhotra.

2. Tape removal

Use a piece of adhesive tape such as duct tape or medical tape and press it gently onto the affected area. Peel it off slowly to lift out any embedded hair. “Repeat this process four-five times, but don’t overdo it, as it can lead to further irritation,” says the expert.

3. Cool compress

Soak a clean cloth in cold water or wrap ice cubes in a towel and apply it to the rash for 10-15 minutes. Cold compress helps reduce swelling, itching, and the burning sensation associated with a caterpillar rash. Reapply as needed throughout the day so that you get some comfort.

4. Baking soda paste

Mix 1-2 tablespoons of baking soda with a small amount of water to form a thick paste. Apply this paste to the rash and leave it on for 10-15 minutes before rinsing with cool water. “Baking soda is good, as it helps neutralise the irritants and provides relief from itching and redness,” says the expert.

5. Oatmeal bath

Add colloidal oatmeal or ground oatmeal to a lukewarm bath and soak your body in it for 15-20 minutes. It can help with itching and skin irritation, as per research published in the Journal of Drugs in Dermatology in 2020. “Oatmeal has natural anti-inflammatory properties that can help to calm the skin and reduce discomfort,” says Dr Malhotra.

6. Antihistamines

Antihistamines that are found pharmacies can help reduce itching and allergic reactions. “They are especially useful for preventing scratching, which can lead to infections,” says the expert. But follow the recommended dosage and consult a doctor if you continue to see the symptoms of a caterpillar rash.

7. Topical corticosteroids

Apply a mild hydrocortisone cream (1 percent) to the rash to decrease inflammation and redness. These creams are widely available without a prescription, but should not be used on broken skin. During a 2011 study published in BMJ Case Reports, using this cream and an orally administered antihistamine helped to make skin lesions and itching caused by a caterpillar disappear within a week.

8. Pain relievers

Nonsteroidal anti-inflammatory drugs like ibuprofen or acetaminophen can help reduce pain as well as swelling associated with a caterpillar rash. “Take these pain relievers with food and water so that your stomach does not get irritated,” says the expert.

A caterpillar rash may last just for a few days, but you can use creams, medicines, and baking soda to get relief soon. Also, monitor the caterpillar rash for signs of infection, such as increased redness, warmth, or pus, and consult a doctor if needed.