When an illness takes hold, the accompanying back pain can feel intense, adding to the discomfort of fever and fatigue. This common experience is typically not a sign of a spinal injury. The aching is frequently a normal byproduct of your immune system actively fighting off an infection. Understanding the biological and mechanical reasons behind this pain clarifies why a simple cold or flu can cause back ache.
The Body’s Inflammatory Response
The primary cause of deep, generalized back pain during a systemic infection is the body’s inflammatory response. When the immune system detects a virus or bacteria, it releases signaling proteins known as cytokines into the bloodstream. These molecules, which include interleukins and interferons, coordinate the immune defense.
Cytokines travel throughout the body, triggering sickness behaviors such as fever, fatigue, and widespread muscle aches (myalgia). They stimulate pain receptors in muscle tissue, including the large muscle groups in the back. This chemical stimulation creates the sensation of a deep, persistent ache.
The lower back is particularly sensitive to these neuroimmune signals, making the pain especially noticeable. High levels of pro-inflammatory cytokines are associated with increased pain intensity. This heightened sensitivity may linger until the inflammatory chemical levels normalize, even after the infection begins to clear.
Physical Strain Caused by Illness
Physical actions associated with being sick place direct mechanical stress on the spine and surrounding muscles. A respiratory illness causing severe coughing and sneezing involves a forceful, sudden contraction of the core muscles. These muscles, including the intercostals and obliques, work with back muscles to stabilize the spine during the explosive action of a cough.
The repetitive nature of a strong cough can strain abdominal and back muscles, leading to localized muscular soreness. Forceful vomiting can also cause significant muscular tension and strain in the torso. These physical overexertions can exacerbate existing minor back issues or create new areas of muscle tenderness.
Fatigue often leads to prolonged rest in slouched positions with poor support. This sustained poor posture places uneven stress on spinal discs and ligaments, contributing to stiffness and pain distinct from the systemic ache. Dehydration, common with fever or vomiting, also contributes to muscle cramps and tension in the back.
Identifying Different Types of Back Pain
When back pain occurs during an illness, it is important to distinguish between generalized muscular ache (myalgia) and localized pain indicating a complication. Myalgia presents as a diffuse, dull ache affecting many muscle groups, often in the lower back, neck, and limbs. This pain typically improves with rest as the infection subsides.
A different presentation is flank pain, felt higher up on one or both sides of the back between the lower ribs and the hips. This location corresponds to the kidneys. Pain here, especially with fever, can suggest a kidney infection (pyelonephritis).
Unlike mechanical back pain, which worsens with movement, kidney pain is often constant and does not change with shifts in posture. Kidney infections require prompt medical attention and may cause sharp or dull pain that radiates toward the abdomen or groin. Recognizing whether the pain is widespread or localized flank pain is crucial for identifying the underlying cause.
Critical Symptoms Requiring Medical Review
While most back pain during illness is related to myalgia or muscle strain, certain accompanying symptoms are red flags requiring immediate medical evaluation.
Urgent symptoms include:
- Back pain combined with a high fever, especially over 103°F, which may indicate a serious infection like a spinal epidural abscess or pyelonephritis.
- Severe, unrelenting back pain that is not relieved by rest or changing position.
- New neurological changes, such as numbness, tingling, or weakness in the legs, suggesting possible nerve compression.
- Sudden loss of bladder or bowel control, which may signal cauda equina syndrome and warrants emergency care.
- Pain accompanied by bloody, cloudy, or burning urination, pointing toward a urinary tract or kidney infection.
A medical professional should also assess the situation if back pain continues to worsen after the primary illness symptoms have resolved, or if the pain is severe enough to wake you from sleep.