A common symptom of Lyme disease is a bullseye-shaped rash. However, many other conditions may cause a similar rash, including ringworm, fixed drug reactions, and allergic reactions to insect bites.

Lyme disease is a bacterial infection that can spread to humans if an infected tick bites a person. Borrelia burgdorferi bacteria are the main cause of Lyme disease.

According to the Centers for Disease Control and Prevention (CDC), there are approximately 30,000 reported cases of Lyme disease in the United States each year.

The most common symptom of Lyme disease is an erythema migrans (EM) rash, which can appear in the shape of a bullseye.

In addition to Lyme disease, a number of other conditions may cause a bullseye-shaped rash. This article outlines some other possible causes of a bullseye-shaped rash and when to contact a doctor.

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Insect bites are commonly not serious, and a person can often treat their bite at home.

If a person has an allergic reaction to an insect bite, it may cause them to develop a rash on the skin that may feel itchy.

People should consult a healthcare professional about insect bite treatments, which may include:

  • topical medication such as hydrocortisone cream or ointment
  • oral antihistamine to reduce the itchiness
  • regular application of a cold compress or ice pack to reduce swelling

A severe allergic reaction to an insect bite can cause a person to experience anaphylaxis, which can be life threatening.

Anaphylaxis: Symptoms and what to do

Anaphylaxis is a severe allergic reaction that can be life threatening. The symptoms develop suddenly and include:

  • hives
  • swelling of the face or mouth
  • wheezing
  • fast, shallow breathing
  • a fast heart rate
  • clammy skin
  • anxiety or confusion
  • dizziness
  • vomiting
  • blue or white lips
  • fainting or loss of consciousness

If someone has these symptoms:

  1. Check whether they are carrying an epinephrine pen. If they are, follow the instructions on the side of the pen to use it.
  2. Dial 911 or the number of the nearest emergency department.
  3. Lay the person down from a standing position. If they have vomited, turn them onto their side.
  4. Stay with them until the emergency services arrive.

Some people may need more than one epinephrine injection. If the symptoms do not improve in 5–15 minutes, or they come back, use a second pen if the person has one.

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A fixed drug reaction is an adverse drug effect that occurs after a person takes a certain medication. It causes a skin lesion, which can look like an EM rash. It may appear on the:

  • extremities
  • lips
  • head and neck
  • genitalia

A person’s reaction typically appears in the same location every time they take the medication.

Treatments for fixed drug reactions may include:

  • discontinuing the medication that is causing the reaction
  • topical corticosteroids
  • oral antihistamines

Ringworm is a skin infection that occurs due to a fungus. It causes a ring-shaped rash on the skin.

Approximately 40 different types of fungi can cause ringworm, including Trichophyton, Microsporum, and Epidermophyton.

Common symptoms of ringworm include:

The treatment for ringworm depends on the location of the infection.

If a person has ringworm on their skin, they can treat it using nonprescription antifungal:

  • creams
  • lotions
  • powders

If a person has ringworm on their scalp, they may need to treat the infection with a prescription oral antifungal medication.

Pityriasis rosea causes a rash that typically clears up on its own without treatment.

Usually, a pityriasis rosea rash begins as a large oval patch on the skin. A person may then develop smaller patches or tiny bumps on their skin.

Experts do not know the exact cause of this rash. However, some research suggests that it may have a link to certain types of human herpes viruses.

A person does not need to treat their pityriasis rosea rash, as it will go away on its own. It may go away within 6–8 weeks or last 5 months or longer.

Granuloma annulare is a skin condition that causes a rash to develop on a person’s skin.

It rarely causes other symptoms, such as itchiness or pain.

There are a number of different types of this skin condition. The most common type of granuloma annulare causes a slightly raised patch of skin that has a noticeable border.

Granuloma annulare may cause a person to develop more than one rash. It can also cause patches that cover a large amount of the body.

Experts largely do not know what causes this condition. However, it has several possible triggers, including:

  • injuries to the skin
  • certain medications
  • the development of another disease

Most people do not need treatment for granuloma annulare, as it usually goes away on its own.

If a person has a number of noticeable patches on their skin, they may make use of one of the following treatments:

  • topical corticosteroids
  • corticosteroid injections
  • cryosurgery, which freezes the skin to destroy the raised patches

Hives is a skin reaction that causes bumps and raised patches to appear on the skin.

They can develop anywhere on a person’s body, most commonly appearing on one or more of the following areas:

  • upper arms
  • chest
  • abdomen
  • back
  • buttocks
  • upper legs

When a person’s immune system recognizes a threat, it releases histamine and other chemicals to help fight infections and protect the person from becoming ill.

In some cases, the immune system releases histamine when there is no real threat. These high levels of histamine may cause a person to develop hives.

Events that may cause the body to release histamine and develop hives include:

  • allergic reactions
  • overreaction to heat, cold, or, sweat
  • stress
  • exposure to sunlight
  • pressure on the skin due to tight clothing or scratching

In mild cases of hives, the rash may go away on its own. However, sometimes a person may need treatments such as:

  • anti-itch lotion or cream
  • antihistamines
  • corticosteroids for severe hives
  • omalizumab
  • light therapy
  • an autoinjector, or EpiPen, for severe allergic reactions

A person with a bullseye-shaped rash on their skin should consult a doctor. This is because the rash may be an early symptom of Lyme disease, which requires treatment with antibiotics.

Other early symptoms of Lyme disease include:

Lyme disease can cause more severe symptoms within months of experiencing an infected tick bite.

People should seek immediate medical attention by calling 911 if someone is experiencing symptoms of a severe allergic reaction, such as:

A bullseye-shaped rash on the skin is a common symptom of Lyme disease.

However, a number of other conditions — including ringworm, fixed drug reactions, allergic reactions to insect bites, and hives — can cause a similar rash.

A person should contact a doctor if they develop a bullseye-shaped rash, as it may require treatment. If a person experiences symptoms of a severe allergic reaction, they or someone nearby should seek immediate medical help by calling 911.