Before understanding the types and patterns of fever, it is essential to know its phases.

• The first stage is the onset/invasion phase, during which the body temperature rises. It might be a sudden or gradual process.
• The second stage is the steady phase, during which the body temperature has reached its maximum and remains constant at a high level.
• The third stage is the defervescence or decline phase, during which the elevated temperature returns to normal. The fever may subside suddenly or gradually.

Fever occurs in various types and patterns. Let us examine them one by one.

1. Intermittent or quotidian fever: The body temperature regularly fluctuates between periods of fever and normal or subnormal temperature. This frequency might range from a few hours to three days. The temperature is usually higher in the evening than in the morning. Example: Malaria, which is known for its characteristic intermittent fever.
2. Remittent fever: temperature fluctuates more than two degrees between morning and evening but does not reach usual. Example: Infections like pneumonia and endocarditis are known to cause remittent fever.
3. Constant or continuous fever: The body temperature remains continuously high and changes by under 2 degrees Celsius. Example: Typhoid fever is a common cause of constant or continuous fever.
4. Relapsing fever is characterized by a temporary return to average body temperature for at least one day, followed by the subsequent recurrence of fever. Example: Tick-borne diseases such as Lyme disease can cause relapsing fever.
5. Crisis: Fever comes to normal after a few hours or days of being extremely high. There are two types of crises: true and false crises. In a true crisis, the temperature drops abruptly within a few hours and returns to normal, accompanied by a significant improvement in the patient's health, for example, fever seen in malaria. In a false crisis, the patient's overall condition does not appear to improve. It might be a warning sign rather than a sign of progress—for example, patients with tuberculosis.
6. Lysis: The temperature drops in a zig-zag pattern for two or three days or a week before returning to normal, when the other symptoms gradually fade. Example: Dengue fever is known for its lysis stage, where the patient's temperature drops for a few days before returning to normal.
7. Inverse fever: the maximum temperature range is recorded in the morning and the lowest in the evening, which is opposed to the typical course of fever. Example: In some cases of malaria, the patient may experience an inverse fever due to the malaria parasite's life cycle, which causes a spike in body temperature during its reproductive stage at night.
8. Hectic or swinging fever: this type of fever occurs when the gap between the high and low points is relatively high. Example: Typhoid fever is characterized by a hectic or swinging fever