Lower back pain is a common complaint when the body is fighting off an infection like the flu or a bad cold. This discomfort can range from a dull, widespread ache to a sharp pain. Understanding the reasons behind this symptom involves looking at the body’s internal fight against the pathogen and the physical stresses of being sick. This helps determine if the pain is a temporary side effect of illness or a sign of a more serious, localized problem.
How the Immune Response Causes Widespread Aches
The generalized discomfort often felt throughout the body during an illness is a direct result of the immune system’s activation. White blood cells release small proteins called cytokines, which act as messengers to coordinate the immune response. These pro-inflammatory cytokines, such as Interleukin-6 (IL-6), circulate through the bloodstream, signaling the brain and other tissues. This signaling process is meant to induce behaviors like fever and fatigue, but it also causes myalgia, or muscle pain. The inflammation caused by these chemical messengers is systemic, affecting the entire body, and often manifests intensely in large muscle groups like those supporting the lower back.
Mechanical Stressors Associated with Illness
Beyond the chemical response, the physical actions associated with being sick place considerable mechanical strain on the lower back. Persistent coughing or forceful sneezing creates a sudden, intense pressure within the abdomen and chest cavity. This action stresses the core muscles and the ligaments and muscles of the lumbar spine, leading to muscle soreness or minor muscle strains.
Even the necessary act of resting can contribute to back discomfort. Spending prolonged periods in bed or slumped on a couch often results in poor posture, which can strain the spinal supporting structures. When the body is fighting an infection, it frequently experiences dehydration due to fever or reduced fluid intake. Dehydration compromises the fluid content of the intervertebral discs, reducing their ability to cushion the spine.
Lower Back Pain as a Sign of Kidney Involvement
While most back pain during illness is muscular, it is important to recognize when it might signal a more serious, localized infection. The kidneys are situated in the back, just below the rib cage on either side of the spine, and an infection there can cause referred pain, known as flank pain. Flank pain is typically felt higher up than common lower back muscle aches. A kidney infection, or pyelonephritis, usually develops when a lower urinary tract infection travels upward. This condition is often accompanied by symptoms that help distinguish it from general body aches, including a high fever, chills, nausea, vomiting, and changes in urination. Kidney pain is frequently described as a deep, constant ache, often localized to one side, which does not change significantly with movement or position, unlike muscular back pain.
When to Seek Medical Attention and Pain Relief
The vast majority of back pain experienced while sick will resolve as the underlying illness runs its course. To manage general muscle discomfort, over-the-counter pain relievers, such as acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, can help reduce both the pain and the systemic inflammation causing it. Applying heat therapy, such as a heating pad or warm bath, can relax tense back muscles. Maintaining adequate hydration and gentle movement can prevent stiffness caused by prolonged bed rest.
Immediate medical attention is warranted if the back pain is accompanied by certain warning signs. These “red flag” symptoms indicate a potentially serious issue that needs urgent evaluation:
- A fever higher than 101°F.
- Pain localized strongly to one side or the flank area.
- Pain paired with persistent vomiting.
- A sudden change in bladder or bowel control.
- Numbness or weakness in the legs.