What are the Causes of Left Side Pain?

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Left side pain, also referred to as flank pain, is a pain that occurs on the left side between the back and upper abdomen. There are several causes of left side pain. Each cause varies in seriousness, but whenever a patient experiences pain in the left side, they should always consult a physician because some causes are serious.

Kidney Infection

Also referred to as acute polynephritis, a kidney infection is simply an infection affecting the kidneys. This infection is a bacterial infection that typically travels to the kidneys, after originating in the bladder or urethra. This infection must be treated quickly to avoid serious complications, such as sepsis or permanent kidney damage. In additional to having pain in the left side, symptoms can include:

  • Fever
  • Back pain
  • Frequent urination
  • Pain or burning when urinating
  • Right side pain (if right kidney is affected)
  • Groin pain
  • Pus or blood in urine
  • Abdominal pain
  • Strong, constant urge to urinate

When a kidney infection is diagnosed in a timely manner, antibiotics are often effective in treating it. When the infection is severe, the patient may require IV antibiotics and to be hospitalized.

Muscle Spasm

Muscle spasms result in cramps and pain and occur when a muscle contracts involuntarily. Many things can cause muscle spasms, such as:

  • Alcoholism
  • Heavy exercise
  • Kidney failure
  • Muscle fatigue
  • Pregnancy
  • Dehydration
  • Hypothyroidism
  • Medications
  • Metabolic problems
  • Reduced levels of blood-calcium and blood-magnesium levels

Muscle spasms cause pain where they are located, such as left side pain, and stiffness. Stretching can help to stop the pain and break the spasm. Medications, such as muscle relaxants and non-steroidal anti-inflammatory drugs can also be beneficial in alleviating pain and stiffness, as well as preventing muscles from spasming in the future.

Side Stitches

This is one of the most common causes of left side pain. This pain is common after running, especially when the person pushes herself too hard or is in poor physical condition. The pain is often sharp and at waist level. It is relieved through slow, deep, regular breathing, applying pressure to the painful area using three fingers, and stopping running.


Also referred to as herpes zoster, this condition is caused by the varicella-zoster virus and is characterized by a blistering, painful skin rash. The pain is typically on one side and can also be tingling and burning. The rash tends to appear after the pain begins. Other symptoms of shingles can include:

  • Abdominal pain
  • Difficulty moving some facial muscles
  • Fever and chills
  • Genital lesions
  • Hearing loss
  • Eye motion loss
  • Taste problems
  • Drooping eyelid
  • Malaise
  • Headache
  • Joint pain
  • Swollen glands
  • Vision problems

Antiviral medications are the most common type of treatment. Some patients will receive this medication via IV, but most take an oral form. Corticosteroids, pain medications, capsaicin-based creams, and antihistamines are often used to help relieve some of the symptoms.


MedlinePlus. (2009). Flank Pain. Retrieved on August 21, 2010 from MedlinePlus: https://www.nlm.nih.gov/medlineplus/ency/article/003113.htm

Wrong Diagnosis. (2010). Side Pain. Retrieved on August 21, 2010 from Wrong Diagnosis: https://www.wrongdiagnosis.com/sym/side_pain.htm