Rashes from amoxicillin: Is it a true allergy?

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Identifying an amoxicillin allergy

When a 1-year-old girl was brought to Texas Children’s for an ear infection, she had a fever of 102, and her pediatrician prescribed amoxicillin. Although she recovered quickly, she woke up on the fifth day of treatment with a mysterious rash that nearly covered her body. Her mother, concerned for her child and confused about the cause of the rash, discontinued the medication. She was unaware of the side effects of amoxicillin or what an amoxicillin allergy may look like. She feared it was a serious reaction and regretted giving her daughter the medication in the first place. 

Unfortunately, her experience is all too common. It is important to know what amoxicillin is and what its side effects are. Read below to learn about amoxicillin rashes, reactions to the medication and how to discern if your child has an amoxicillin allergy, as well as recommended treatments.

What is amoxicillin and what is amoxicillin used for?

Although amoxicillin is a common medication, many people don’t know what amoxicillin is used for. Amoxicillin is a widely prescribed antibiotic that effectively treats bacterial infections in both children and adults. As a member of the penicillin class of medications, amoxicillin works by inhibiting the growth of bacteria, allowing the immune system to efficiently eliminate the infection. Amoxicillin does not treat the common cold or flu.

Doctors often prescribe amoxicillin to treat many conditions such as bronchitis, pneumonia, sinusitis, and strep throat. The medication is available in various forms, including capsules, tablets, chewable tablets, and liquid suspensions, making it accessible and convenient for patients of all ages.

Amoxicillin is commonly used to treat a variety of bacterial infections, including:

• respiratory tract infections
• ear, nose, throat conditions
• urinary tract infections (UTIs)
• skin infections

What to know when taking amoxicillin

To ensure the effectiveness of the treatment and to prevent antibiotic resistance, it is crucial to follow the prescribed dosage and complete the full course of amoxicillin. Proper adherence to the medication regimen helps to fully resolve the infection and maintain overall health. When taking amoxicillin, it’s important to be aware of potential amoxicillin side effects. Amoxicillin can stay in your system for 12 hours after taking a dose and you can have side effects after stopping the medication.

A rash is the most common amoxicillin side effect. About 5 to 10 percent of children taking amoxicillin or Augmentin will develop a skin rash during the course of their medication. Most of these rashes are non-allergic and are typically caused by viruses.

So, how can you tell the difference in amoxicillin rash vs amoxicillin allergy?

Can amoxicillin cause a rash?

Amoxicillin can case a rash as a side effect in both men and women. Having a rash is relatively common amoxicillin side effect and the degree of the reaction can vary in children and adults. An amoxicillin rash can manifest in two forms: allergic and non-allergic. A rash from amoxicillin can last up to a week but typically goes away sooner and how it looks varies on the person and whether it is an amoxicillin allergy or rash.

An amoxicillin rash can show up immediately after starting the medication. In addition, it’s possible to have a delayed allergic reaction to amoxicillin that shows up days after taking the medication. If you or your child develops a rash or has other side effects from antibiotics or medications, be sure to consult your doctor.

Amoxicillin rashes can manifest in various forms, including:

• Maculopapular Rash: Characterized by flat, red patches and raised bumps spread over the body.
• Hives (Urticaria): Itchy, raised red or skin-colored welts that can change shape and location.
• Erythema Multiforme: More severe, featuring target-like lesions or bull's-eye shapes with a central red spot, pale ring, and red outer ring.
• Anaphylactic reaction: This is a rare but severe allergic reaction that includes symptoms like difficulty breathing, swelling of the face, lips, or tongue, hives, and a rapid drop in blood pressure. This reaction requires immediate medical attention.

By staying informed about the potential side effects of amoxicillin, you can take proactive steps to address any adverse reactions and maintain overall health. If you or your child develops a rash while taking amoxicillin or after taking amoxicillin, it is crucial to consult with a healthcare provider to determine the cause and appropriate treatment. Understanding these reactions and amoxicillin side effects can help manage symptoms effectively and ensure safe use of the medication.

How long does an amoxicillin rash last?

An amoxicillin rash in adults or children typically lasts for about 3-10 days. Although an amoxicillin rash usually resolves in a week, it can last up to two weeks. A rash caused by amoxicillin usually shows up within the first few days of taking the medication, but it’s possible to have a delayed amoxicillin rash or reaction. Contact your doctor if you experience a rash as a side effect of taking amoxicillin. Your doctor can inform you about the rash and how long it may last, depending on your conditions.

Non-allergic amoxicillin rash, reaction signs and side effects 

A non-allergic rash often appears as flat, red spots that may be slightly raised and is generally not harmful. A non-allergic rash occurring while taking amoxicillin or Augmentin may have similar side effects.

A non-allergic amoxicillin rash reaction will look like:

• The amoxicillin reaction may look like small (less than half an inch) widespread pink spots in a symmetrical pattern or slightly raised pink bumps
• Usually appear on day 5-7 from the start of the amoxicillin or Augmentin, but can occur at any time during the course of the medication
• It always appears on the chest, abdomen or back and usually involves the face, arms and legs - the rash may worsen before it gets better
• The rash differs from differs from hives in appearance (hives are always raised, itchy and change location) 
• Usually goes away in three days, but can last from one to six days 
• It’s not contagious, so he/she can go back to school

Allergic reaction to amoxicillin - Warning signs

The warning signs that a true allergic reaction is occurring would be sudden onset of the rash within two hours of the first amoxicillin dose, any breathing or swallowing difficulty or very itchy hives. An allergic amoxicillin rash is typically characterized by hives or red, itchy patches and may be accompanied by other symptoms such as difficulty breathing or swelling, indicating a more serious reaction.

Even if you know it’s not an allergic reaction to amoxicillin, it may still feel wrong to continue the amoxicillin medication or give it again in future. There are several reasons why it is better to continue using amoxicillin than stopping or changing to a different antibiotic:

• Changing to a broader-spectrum antibiotic may not be necessary and could cause other problems, such as diarrhea or vomiting. 
• Stopping the medication can incorrectly label your child as allergic to the penicillin-family of antibiotics, which would limit future antibiotic choices. 

If your child is on amoxicillin or Augmentin and develops a rash or has other side effects, always consult your pediatrician. Anytime you suspect an allergic reaction to antibiotics, always consult a medical professional. If considered appropriate by your pediatrician, you can be evaluated by an allergist to assess if future avoidance is needed.

What causes amoxicillin rash or allergy?

An allergic reaction to amoxicillin, or any other kind of medication, is caused by one’s immune system reacting to that medication as if it were a foreign invader in the body. This reaction to amoxicillin most commonly causes a rash known as hives, or whelps, which are itchy, can come and go, and appear in varying parts of the body. This rash typically develops soon after a patient starts to take the medication (within the first 1-2 doses), and may linger for days to weeks. Learn more about hives and rashes in children.

In contrast, an amoxicillin rash is a flat rash that typically appears several days after starting the antibiotic. This kind of rash always appears on the chest, abdomen, or back, and can also involve the face, arms and legs. What causes this kind of rash is not always apparent, but in some cases the rash is presumed to be caused by a virus. It is not unusual for a child to start with a viral infection, such as a typical cold, and develop a secondary infection, which may be caused by a bacteria. In such cases, amoxicillin may then be given to treat that secondary infection. Viruses can cause skin rashes that appear while one is taking amoxicillin. These rashes are not itchy and can persist for a few days. This kind of rash is not considered to be harmful.

Amoxicillin rash treatment

If a true allergic reaction is considered, one should immediately stop taking that medication and discuss with their physician. More severe forms of allergic reaction can cause chest tightness, breathing problems and/or GI symptoms. For hives, giving an antihistamine, such as diphenhydramine (Benadryl) may help relief the itching and calm down the hives. Over-the-counter medications can help with fevers, allergies and other amoxicillin side effects.

In contrast, an amoxicillin rash is not considered to be harmful, and — except for observation and patience — there is no treatment for this kind of rash. For this type of rash, it is not necessary to discontinue taking the amoxicillin. An amoxicillin rash is not contagious. Unfortunately, when someone develops such a rash, they may think they are having an allergic reaction and stop taking the medication and consider themselves to be allergic to the medication. This can lead to their physician labeling them as allergic, thus leading to the patient being given different antibiotics — potentially causing more harmful side effects.

Bottom line- if you or your child develops a rash while taking amoxicillin, or any kind of antibiotic or medication, it is best to contact your physician.

If you’re in Houston or Austin, Texas, contact Texas Children’s Hospital to find a pediatric location to help your child with an amoxicillin rash, allergic reaction rash or other side effects. Learn more about our allergy and immunology department and how we help children with allergies.