A fever at night that is gone in the morning is usually the result of the functioning of the hypothalamus, which is a part of the brain the regulates body temperature. The hypothalamus works in a cycle, and becomes more active at night, which can lead to increased body temperature. This is normal, although the hypothalamus can be even more triggered due to a health condition, like an infection or inflammation somewhere in the body (like a cold or strep throat) or a more serious disease like lupus, HIV or cancer.

People tend to notice a fever during the day when they are awake, as fevers usually emerge with other symptoms like intense headache or generalized muscle pain. However, a fever can worsen at night for many reasons, and can make you wake up suddenly from excessive sweating or chills.

Fevers should always be assessed by a doctor, no matter the underlying cause. You should especially seek medical attention if your fever persists for over 3 days or if it does not improve with analgesics or with home remedies, like placing cold compresses on your forehead or eucalyptus tea.

Why do fevers worsen at night and are gone in the morning?

In most cases, fevers emerge or worsen at night due to the cyclic functioning of the hypothalamus. The hypothalamus is a part of the brain that is responsible for producing hormones that regulate body temperature. It becomes more active at night, which can lead to an increase in body temperature when you are sleeping.

In addition, due to normal metabolic functioning, it is normal to expect an increase in body temperature as the day progresses. Temperature hits a peak at night time, which can lead to increased sweating.

Fevers at night are rarely a sign of a serious health problem, and are usually related to an infection. Nonetheless, if you experience night fevers for more than 3 days, you should see a doctor for assessment, as you may need targeted treatment to treat the underlying cause.

Common causes

A fever is one of the body’s natural defense mechanisms and can occur for many reasons, such as:

Viral infection, like a cold, flu or COVID-19
Bacterial infection
During an auto-immune disease flare-up, like rheumatoid arthritis or Crohn’s disease
As a side-effect of certain medications that decrease immune system functioning
Following a vaccine

It is important to identify the underlying cause of the fever, so that appropriate treatment can be started as necessary. Read more about other common causes of night sweats and what to do.

What to do

To treat fevers that are caused by infectious, it is important to first determine the infectious agent, as this will ultimately guide treatment. The doctor can prescribe antibiotics, anti-inflammatories, anti-pyretics and/or antivirals to eliminate the infection, which will then treat the fever.

When treating a fever, you should also opt for well-ventilated rooms and light clothing, and be sure to rest and bathe in warm water. Read more about how to break a fever at home and when you should see a doctor.

When are night fevers serious?

Night fevers are rarely a sign of a serious health condition, even if the underlying cause is not totally known. These types of fevers are most commonly triggered by environmental factors, like increased room temperature or using too much clothing, both which can accelerate systemic metabolism.

There are some illnesses, however, in which daily night fevers are one of the only symptoms. Some examples include:

Lyme disease
HIV
Tuberculosis
Hepatitis
Lupus

Some types of cancer can also initially present with night fevers, however other symptoms eventually emerge, like weight loss for no apparent reason.