The most common cause of a circular rash on the skin is ringworm, but other issues — such as Lyme disease and granuloma annulare — can also leave this distinctive mark.
A doctor diagnoses the cause of a rash after examining it and asking about symptoms. They may recommend oral medication, a topical cream, or strategies for avoiding triggers.
In this article, learn more about the issues that can cause this rash and how to treat them.
Despite its name, ringworm is a fungal skin infection — it is not caused by a worm or any other parasite.
The infection got its name because it causes a rash that is usually circular, with a thin raised ring around the edge that may look like a worm.
The circular rash may initially measure a few centimeters across, and it can grow without treatment. It may look like a round, flat patch, and the middle of the rash tends to heal first.
On lighter skin, a ringworm rash is red or pink, and on darker skin, it is silver or brown.
The skin around the rash may be dry or scaly, and the rash can be extremely itchy.
Ringworm can appear on any part of the body, and the rash may not be ring-shaped if it appears on the scalp, soles of the feet, palms, groin, or nails. Athlete’s foot and jock itch are types of ringworm.
Ringworm is infectious and can pass from one person to another through close contact.
How long is ringworm contagious for? Find out here.
Treatment involves antifungal cream or gel. A person should:
- Use the medication for 2–4 weeks, even after the symptoms go away.
- Keep the skin as clean and dry as possible.
- Wash the hands after touching the rash to keep it from spreading to other parts of the body.
The risk of developing ringworm is higher in warm, humid weather. To reduce the chances:
- Always shower after exercise.
- Change clothes daily.
- Do not share towels or brushes.
- Take any pet that develops bare patches of fur or other ringworm symptoms to the vet.
After a tick bite, a circular rash may develop at the site. This is an early symptom of Lyme disease.
The circular rash can appear days or weeks after the bite, and it may have a distinctive bull’s eye appearance.
On lighter skin, a person may see three circles surrounding the bite: a red circle closest to the bite, then a lighter ring, then another red ring. On darker skin, the appearance can be different — check for a raised ring around the bite.
The rash usually expands over time. It can cause pain, burning, or itching, and it may be warm to the touch.
A tick may bite any part of the body, and it may favor exposed or warm areas. These bites are common in the lower leg, armpit, groin, and back.
About half of the people who contract Lyme disease have flu symptoms, which usually appear before the rash.
Receiving treatment early on is crucial. At an initial stage, a course of antibiotics can cure Lyme disease.
Check the skin for tick bites after being outdoors. Remove a tick right away, without squeezing it, and be sure to remove the tick entirely.
Contact dermatitis is an allergic skin reaction.
The skin will darken or redden and may feel itchy or dry. Contact dermatitis can also cause the skin to swell or blister.
The size of the rash depends on how much skin has come into contact with the allergen.
The rash may be circular if the object triggering the reaction is round. For example, if a person has a nickel allergy, wearing a nickel watch may cause a round rash to form on the wrist.
The most effective way to combat contact dermatitis is to identify and avoid contact with the allergen or irritant.
It can help to use products designed for sensitive skin and to check labels of soaps and personal care products carefully for common allergens and irritants.
Over-the-counter creams can help reduce swelling and irritation.
Hives are a reaction to temperature, food, medication, viral infections, and other triggers.
Hives form when the skin swells into welts. These are red or skin-colored bumps or patches that may itch or burn.
Hives can develop on any part of the body, and they may appear and disappear quickly. In some people, hives or patches of hives may be circular and resemble bug bites.
Antihistamines can reduce swelling and prevent hives if they result from contact with an allergen.
If hot weather is a trigger for hives, wear loose clothing, and use sunscreen. Also, it may help to dampen the skin with a wet washcloth.
Granuloma annulare is rare. It causes bumps to form a circular or ring-shaped rash.
The rash most often appears on the hands, arms, or feet. Less commonly, it can spread across the body, or smaller patches can join to form larger ones.
The causes are still unclear, but granuloma annulare can develop after skin damage or a viral infection.
Granuloma annulare causes no symptoms beyond the rash, and it is not contagious.
The condition usually disappears without treatment, but it can last for years. Steroid injections or creams may help the body heal.
If any circular rash lasts for a long time, causes significant discomfort, or affects the face or throat, a person should see a doctor.
If ringworm doesn’t go away after 2 weeks of treatment, see a doctor.
If it affects the scalp, however, it is a good idea to consult a doctor or pharmacist right away. Also, anyone who has a weakened immune system should see a doctor if they have ringworm.
If an allergic reaction is severe or the cause is unclear, seek professional guidance.
Always see a doctor about a tick bite, unless the tick was safely removed within 36 hours of the bite.
Seek urgent medical care if a rash:
- covers the entire body
- occurs with a fever
- is painful
- begins to blister
- occurs with difficulty breathing
A doctor, such as a dermatologist, will consider accompanying symptoms and any contact with allergens or irritants when diagnosing a circular rash.
Allergists can test for triggers of skin reactions, which are often pet hair or medication.
They may test the skin, blood, or urine, but they commonly perform patch tests. This involves placing strips containing small amounts of allergens on the back. The doctor then removes the strips after 48 hours to check for an allergic reaction.
Keeping track of foods, drinks, medications, physical activities, and symptoms in a diary can help a person identify what might be triggering a reaction.
The size and shape of a circular rash and the symptoms it accompanies can each point to the cause.
A person can treat mild cases of ringworm, hives, and contact dermatitis with home care and over-the-counter products. However, if a circular rash is severe or may result from a tick bite, see a doctor.
It is also important for a person to receive professional care if they have had an allergic reaction without an obvious cause.
Anyone with a persistent rash or other skin problems may benefit from seeing a dermatologist.