Unexpected Side Effects of Having a High Fever

Amy Barczy

| 4 min read

Man lying on the couch with a high fever checks a thermometer
Fevers occur when the body’s temperature rises as a part of its immune response. While fevers can be scary, they are a normal part of the body’s reaction to infection.
Fevers often occur with other symptoms, depending on what’s causing the infection. These symptoms can all be uncomfortable, but typically there is no major cause for alarm for adults. In children and infants, it’s important to watch their temperature. For infants, a low fever can be a sign of a more serious infection.
A temperature of 98.6 degrees F is the average temperature for children and adults. What is considered a high fever varies depending on the person’s age:
  • Adults: An oral temperature of 100 F or higher is considered a fever. An oral temperature of 103 F or higher is considered a high fever, and you should seek medical attention.
  • Children: An oral temperature of 100 F or higher is considered a fever. An oral temperature of 102 F or higher is considered a high fever, and you should seek medical attention as fevers at 104 F or higher could cause seizures.
  • Infants: Seek medical attention immediately if an infant under the age of three months has a rectal temperature of 100.4 F or higher. Call a doctor right away if an infant age three to six months has a higher-than-normal rectal temperature and is irritable or sleepy. Infants aged three months to children aged 24 months should be seen by a doctor if they have a rectal temperature of 102 F or higher, especially if other symptoms are present.

Side effects of having a high fever

High fevers can result in some unexpected side effects.
  • Sweating after the fever breaks: After the peak of a fever, the body begins to bring its temperature back down to normal and may begin to sweat profusely. It’s the body’s way of trying to cool itself and return back to normal again.
  • Rash in toddlers: Some toddlers can develop a rash after several days of a high fever. This is most commonly caused by a virus, including roseola, hand foot and mouth disease, and fifth disease.
  • Hair shedding: Due to the extreme stress the body experiences due to an illness and fever, the body can shed hair. This can occur two to three months after having a fever or illness. This hair shedding is temporary.
  • Cold sores: A fever can trigger a cold sore in people who are susceptible to them. Some people call them “fever blisters.”

When to see a doctor

Talk to a health care provider right away if the high fever thresholds are reached. While there are medications to help manage the fever symptoms, it’s important to address the source of the fever as it may be a sign of a more serious health condition or infection. Some infections are caused by bacteria that can be managed through antibiotics, which must be obtained through a provider’s prescription.
If an infant or child has a seizure after a fever, seek medical attention immediately. Children over the age of two that have a fever with additional symptoms including rash, discomfort, irritability, listlessness, headache, stiff neck, or diarrhea and vomiting should also be seen by a health care provider. Fevers accompanied by a skin rash, as well as difficulty or rapid breathing, should also be a cause for concern.
If you have questions about when to see a doctor, Blue Cross Blue Shield of Michigan and Blue Care Network members can access a medical professional 24/7 by calling the 24-Hour Nurse Line. 
PPO Plans – Blue Cross Blue Shield of Michigan
  • 1-800-775-BLUE (2583)
HMO Plans – Blue Care Network
  • 1-855-624-5214

Managing a fever at home

While managing a fever at home, it’s important to stay hydrated by drinking clear liquids including water, broth, juice or a sports rehydration drink. Rest and stay cool with lightweight clothing and bed linens. Talk to your health care provider about what over the counter medications can help you manage the fever.
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Photo credit: Getty Images

A Healthier Michigan is sponsored by Blue Cross Blue Shield of Michigan, a nonprofit, independent licensee of the Blue Cross Blue Shield Association.
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