A fever is an elevated body temperature, typically defined as above 100.4°F (38°C). It functions as a biological sign that the body is activating its defense mechanisms against a perceived threat. This rise in temperature is not the illness itself but a controlled response, usually orchestrated by the brain’s hypothalamus, to create a less hospitable environment for pathogens. While many assume a fever remains consistently high, temperatures often fluctuate, leading to the observation that a fever comes and goes throughout the day or over a longer period. This cyclical change is a significant clue that helps medical professionals identify the nature of the underlying issue.
Understanding Intermittent and Relapsing Fever Patterns
The phenomenon of a fluctuating temperature is categorized into distinct clinical patterns that provide initial diagnostic direction. An intermittent fever is characterized by temperature spikes that alternate with periods where the body temperature returns completely to a normal baseline, usually within a 24-hour cycle. The temperature drops back to 98.6°F (37°C) before rising again the next day, a pattern often seen in localized or acute infections.
A different pattern is the relapsing fever, which involves prolonged episodes of fever lasting several days, followed by intervals of normal temperature that can last for days or even weeks. During the fever-free interval, the patient feels relatively well before the fever returns in a subsequent spike. This longer cyclical pattern is associated with specific systemic conditions or infections.
Common Infectious Causes
The most frequent reasons for an intermittent fever pattern are common, often self-limiting, infections where the body is actively managing the fight. Many viral infections, such as the common cold or flu, cause a fever to spike, drop as the immune system gains temporary control, and then spike again, especially toward the evening. This fluctuation reflects the daily rhythm of the body’s immune response and the natural cycle of the hypothalamus, which often causes a slight temperature increase in the late afternoon or evening.
Localized bacterial infections are also a frequent cause of this type of fluctuation, particularly those affecting ducts or confined spaces, such as urinary tract infections (UTIs) or abscesses. The body cycles through periods of intense inflammatory response, causing the temperature to rise, followed by temporary dips as the immune system briefly contains the infection. Furthermore, taking fever-reducing medications like acetaminophen or ibuprofen artificially creates an intermittent pattern by temporarily overriding the body’s temperature regulation.
Systemic and Chronic Conditions
Less common, but often more serious, conditions are associated with the longer, relapsing fever pattern or pronounced daily spikes. Relapsing fever is classically linked to specific bacterial infections caused by Borrelia species, transmitted by ticks or lice. The bacteria repeatedly change their surface proteins to evade the immune system, leading to recurrent episodes of high fever separated by afebrile periods. Malaria also produces a highly regular intermittent or relapsing pattern, with fever spikes occurring every 48 or 72 hours, depending on the specific parasitic species involved.
Beyond infections, systemic inflammatory conditions are a significant cause of cyclical fevers. Certain autoimmune disorders, such as Adult-onset Still’s disease, can cause a quotidian fever—a single, high temperature spike that occurs around the same time each day, often in the late afternoon. Additionally, autoinflammatory diseases, including Periodic Fever, Aphthous Stomatitis, Pharyngitis, and Adenitis (PFAPA) syndrome, cause fevers that recur with regularity, often every few weeks, without an infectious trigger. These chronic causes require specialized diagnostic testing.
Monitoring Symptoms and When to Seek Help
When experiencing a fever that comes and goes, tracking the temperature and the timing of the cycles provides valuable information to a doctor. Note the time of day the fever spikes, the duration of the fever episode, and the length of the fever-free interval. This record helps determine if the pattern is intermittent, relapsing, or otherwise significant. Monitoring for any accompanying symptoms that arise during the febrile periods is also helpful.
A medical consultation is advised if the fever persists for more than 72 hours, or if the fever-free periods begin to shorten over time. Immediate attention is necessary if the fever is accompanied by “red flag” symptoms that suggest a severe underlying issue. These warning signs include:
- Severe headache
- Neck stiffness
- Confusion
- Difficulty breathing
- Unexplained rash
- Inability to keep fluids down due to persistent vomiting
Seeking professional evaluation ensures that serious causes are identified and treated promptly.