Getting sick and getting lower back pain at the same time is not a coincidence. When your body fights an infection, it releases chemicals that cause inflammation and achiness throughout the body, and the lower back is one of the most common places people feel it. Muscle aches tied to illness usually show up alongside fever, fatigue, and other symptoms, and they tend to fade as the infection clears.
That said, not every case of lower back pain during an illness is simple muscle achiness. Some infections directly affect the spine, kidneys, or nerves, and those situations need medical attention. Knowing the difference matters.
Why Do I Get Lower Back Pain When Im Sick?
The most common reason is the body’s immune response. When you get an infection — whether it is a cold, the flu, COVID-19, or a stomach bug — your immune system releases proteins called cytokines. These chemicals help coordinate the attack on the pathogen, but they also cause widespread inflammation. That inflammation makes muscles and joints feel sore and achy.
The lower back is especially vulnerable because it carries most of your body weight and supports nearly every movement. When your muscles are already inflamed and you are lying in bed more than usual, the lower back is often where the soreness settles. This type of pain is usually dull, spread across a wide area, and gets better as you recover.
Fever makes it worse. A higher body temperature increases blood flow and metabolic activity in tissues, which can amplify the achiness you feel. Dehydration from fever, vomiting, or diarrhea also plays a role. Muscles need fluids and electrolytes to function normally, and when those drop, cramping and soreness become more likely.
What Types of Illnesses Cause Lower Back Pain?
Many common illnesses cause body aches that include the lower back. Influenza is well known for this. So are COVID-19, mononucleosis, and other viral infections. Even a simple cold can leave you feeling achy, especially if you have a fever.
Some illnesses cause back pain for reasons beyond general inflammation:
- Kidney infections (pyelonephritis) often cause pain in the flank or upper back that can wrap around toward the lower back. This pain is usually one-sided and comes with fever, chills, and painful urination.
- Urinary tract infections can cause lower back discomfort, especially if the infection has moved up to the kidneys.
- Spinal infections such as discitis or vertebral osteomyelitis are rare but serious. They cause localized, constant pain that worsens at night and does not improve with rest.
- Shingles can cause burning or shooting pain in the lower back before a rash appears. The pain typically affects one side of the body.
Most people with a viral illness and lower back pain do not have a spinal or kidney infection. But if the pain is severe, one-sided, or comes with other warning signs, it needs to be checked.
How Do You Tell Normal Body Aches From Something Serious?
Normal body aches from illness feel like soreness spread across multiple areas. They improve when the fever goes down and get better as you recover. The pain is usually not sharp or stabbing.
Warning signs that suggest something more than routine achiness include:
- Pain that is severe and stays in one specific spot
- Fever that does not improve or keeps coming back
- Pain that wakes you at night or does not improve with rest
- Numbness, tingling, or weakness in the legs
- Loss of bladder or bowel control
- Pain with urination or blood in the urine
- A visible rash along one side of the back
Any of these signs warrants prompt medical evaluation. Loss of bladder or bowel control combined with back pain is a medical emergency and requires immediate care.
Does Bed Rest Make Lower Back Pain Worse When You Are Sick?
Prolonged bed rest can make back pain worse, even when you are sick. When you lie in one position for hours, your back muscles stiffen and weaken. The muscles that normally support your spine are not being used, so they become tight and sore.
This does not mean you should push through illness and stay active. When you have a fever or are genuinely unwell, rest is appropriate. But changing positions regularly, getting up to walk briefly when you can, and using pillows to support your lower back can reduce stiffness.
Once the acute illness passes, gradually returning to normal movement helps. Prolonged inactivity beyond what the illness requires tends to slow recovery rather than speed it up.
What About Kidney Infections and Lower Back Pain?
Kidney infections are one of the more important causes to rule out when lower back pain happens during an illness. The kidneys sit in the upper abdomen, toward the back, on either side of the spine. When they are infected, pain often shows up in the flank — the area between the ribs and the hip — and can radiate toward the lower back.
Key differences from ordinary body aches:
- Kidney pain is usually one-sided
- It often comes with fever, chills, nausea, or vomiting
- Urination may be painful, frequent, or cloudy
- The pain does not improve with rest or position changes
Kidney infections require antibiotics and can become serious if untreated. If you have lower back pain with fever and urinary symptoms, see a doctor promptly.
What Helps Lower Back Pain When You Are Sick?
Treatment depends on what is causing the pain. For ordinary body aches from a viral illness, the focus is on supporting recovery:
- Stay hydrated. Fever, sweating, vomiting, and diarrhea all cause fluid loss. Water and electrolyte drinks help replace what is lost.
- Use over-the-counter pain relievers if appropriate. Acetaminophen and ibuprofen can reduce fever and achiness. Follow label directions. Check with a doctor if you have liver or kidney conditions, stomach ulcers, or take other medications.
- Apply heat. A heating pad or warm shower can relax tight muscles. Do not use heat on an area with a rash or swelling.
- Change positions regularly. Even small movements help prevent stiffness.
- Sleep with support. A pillow under your knees or between your legs can reduce strain on the lower back.
If the pain is from a kidney infection or spinal infection, those treatments are different and require medical care. Do not try to manage a suspected infection at home with rest and pain relievers alone.
When Should You See a Doctor?
See a doctor if lower back pain during an illness is severe, one-sided, or does not improve as your other symptoms get better. Also seek care if you have a fever that lasts more than a few days, pain that wakes you at night, or any numbness or weakness in your legs.
Go to emergency care immediately if you lose control of your bladder or bowels, or if you cannot walk because of the pain.
Most lower back pain that comes with a cold or flu resolves on its own within a few days to a week as the illness runs its course. If it does not, that is a signal to get checked.
Frequently Asked Questions
Can a cold or flu cause lower back pain?
Yes. Viral illnesses trigger inflammation throughout the body that commonly causes muscle aches, including in the lower back. This type of pain usually improves as the infection clears.
How long does lower back pain from being sick last?
For most viral illnesses, body aches including lower back pain improve within a few days to a week. Pain that lasts longer or gets worse should be evaluated by a doctor.
How do I know if my lower back pain is from my kidneys?
Kidney pain is typically one-sided and comes with fever, chills, or urinary symptoms like burning or cloudy urine. It does not improve with rest or position changes.
Should I go to the doctor for lower back pain with a fever?
If the fever is high, lasts more than a few days, or comes with severe one-sided back pain, yes. These signs can point to a kidney or spinal infection that needs treatment.
