When should someone seek medical care for a fever?

A fever over 104 F/40 C in children and adults is considered dangerous. Seek medical attention immediately.

Any child below 3 months of age who has a temperature of 100.4 F (38 C) or greater should be seen by a physician. If a child or adult has a history or diagnosis of cancer, AIDS, or other serious illness, such as heart disease, diabetes, or is taking immunosuppressant drugs, medical care should be sought for a fever.

Children with a fever who have signs and symptoms such as rash, sore throat, ear pain, stiff neck, drowsiness, fussiness, or headache should see a doctor. In addition, if a fever lasts more than one day in a child or toddler 2 years of age or under, or last more than three days in a child over age 2, seek medical care.

Otherwise, observe the person with the fever. If he or she appears sick or has symptoms that would suggest a major illness, such as meningitis (headache, stiff neck, confusion, problems staying awake), urinary tract infection (shaking chills, back pain, burning with urination), pneumonia (shortness of breath, cough), or any other signs of a serious illness, contact a health care professional.

Other symptoms that may be indicative of a severe illness include repeated vomiting, severe diarrhea, or skin rashes (that could be a sign of dengue fever, Rocky Mountain spotted fever, scarlet fever, rheumatic fever, strep throat, or chickenpox).

Fever blisters (herpangina) are small blisters that turn into ulcers, usually on the lips, mouth, or tongue; a virus causes fever blisters. When a child contracts this virus for the first time, the symptoms and the fever blisters can be quite severe. If the child is not eating or drinking, contact the child’s pediatrician.

Women who are pregnant should contact a doctor for a fever over 101 F (38 C). A fever during pregnancy that is accompanied by a rash and joint pain could be a sign of an infection that could affect the baby. Some infections, such as cytomegalovirus (CMV), can cause congenital deafness and other problems in the baby. If a pregnant woman contracts the Zika virus (also called Zika fever), it may cause a birth defect called microcephaly (small head).

On the other hand, if the fever accompanies a simple cold or virus, one can treat the fever as described above and be assured the fever is only a symptom of the illness. This is not to say one should ignore a fever. If there are other associated symptoms that are bothersome, contact a doctor.

Some vaccines given in childhood can cause a low-grade fever within a day or two of getting the injection. This fever is usually self-limited and short-lived. If the reaction seems severe or the skin at the injection site is red, hot, and painful, contact the child’s doctor.

A low percentage of all children and toddlers between 18 months to 3 years of age will have a seizure (convulsion) with a high fever. Of those with a history of febrile seizure, some will have another seizure associated with another febrile (fever) episode. Febrile seizures, while frightening to the parents, are not associated with long-term nervous-system complications. Children used to be prescribed the antiseizure drug phenobarbital (Solfoton, Luminal) following a febrile seizure as a preventive measure (prophylaxis). This has not been shown to be beneficial and possibly may be harmful, so it is not recommended.

Recurrent fever in children (three or more episodes of fever in a six-month period, with no apparent causative illness) can be a symptom of a few different illnesses, such as PFAPA (periodic fever, aphthous ulcers, pharyngitis, and adenopathy) syndrome, cyclic neutropenia, Epstein-Barr virus (EBV) infection, and others. See your child’s pediatrician if fevers are recurrent.

Recurrent, persistent, or chronic fever in adults may accompany immune-deficient fever of unknown origin (FUO), also known as neutropenic FUO, and HIV-associated FUO, as well as many other infectious conditions. Adults should see their doctors if they develop recurrent fever.