Side Pain: Causes on the Left and Right, and When to Worry

What counts as side pain

Doctors divide the body into regions to narrow down causes. "Side pain" usually means one of three areas:

• Flank: the back half of the side, below the ribs and above the hip. This is where the kidneys sit. Pain here is called flank pain, and kidney stones and kidney infections are its main serious causes; our guide to flank pain in the kidney area covers it in detail.
• Lateral abdomen: the front half of the side, over the colon and, lower down, the ovaries.
• Lower chest wall: the lower ribs and the muscles between them.

Knowing exactly where it hurts, what the pain feels like and what makes it worse narrows the list quickly. Muscle pain is sore to press and hurts when you twist. Kidney pain is deep, often comes in waves and does not change with movement. Bowel pain is crampy and often linked to eating or bowel movements.

Common causes of side pain

These cause most side pain and are usually not dangerous.

• Muscle strain: an overworked or pulled muscle in the side or back. It follows lifting, twisting, sport or a bout of coughing. The area is tender to press and hurts when you bend, twist or breathe deeply. See muscle strain.
• Side stitch (exercise-related transient abdominal pain): a sharp, cramping pain under the ribs during running or swimming, often after eating or drinking. It fades within minutes of stopping.
• Trapped gas and bloating: crampy pain that moves around and eases after passing gas or a bowel movement. The upper left side, under the ribs where the colon bends, is a common spot.
• Constipation: a dull ache on the left side, where stool collects in the descending colon, with hard or infrequent stools.
• Rib and cartilage pain: costochondritis or a bruised rib causes sharp pain when you press on the spot, cough or take a deep breath.
• Shingles: burning or tingling pain in a band on one side of the trunk, followed a few days later by a blistering rash.

Serious causes of side pain

Left side pain: causes and when to worry

Upper left side

• Gas trapped in the splenic flexure (where the colon turns down under the ribs): crampy and relieved by passing gas.
• Stomach problems: gastritis or an ulcer causes burning pain higher up, under the ribs, often linked to meals.
• Pancreatitis: severe upper belly pain that bores through to the back, with vomiting. Common triggers are heavy alcohol use and gallstones. See pancreatitis.
• Spleen problems: an enlarged or injured spleen hurts under the left ribs. Pain after a blow to the left side, especially in someone with recent mononucleosis, needs urgent assessment.
• Left kidney: stones or infection cause pain in the back and side below the ribs.
• Heart and lungs: pneumonia, pleurisy or a pulmonary embolism can cause lower left chest pain that is worse with breathing. Heart pain is usually central but can spread to the left side.

Lower left side

• Constipation and gas: the most common causes.
• Diverticulitis: the most common serious cause in adults over 40. Expect steady pain, fever and tenderness.
• Irritable bowel syndrome: recurring cramps linked to bowel movements, with diarrhea, constipation or both.
• Ovary and fallopian tube (in women): ovarian cysts, ovulation pain (midway through the cycle), ectopic pregnancy, and pelvic infection.
• Inguinal hernia: a bulge and ache in the groin that is worse on straining.
• Testicular problems (in men): pain from the testicle can be felt in the lower side. Sudden testicular pain is an emergency.

When should you worry about left side pain?

Worry, and get care the same day, if left side pain is severe or getting worse over hours, or comes with fever, vomiting, blood in your stool or urine, a swollen or rigid belly, or dizziness. Call 911 or your local emergency number for sudden severe pain with fainting, chest pain, or breathlessness. Pain with a possible pregnancy always needs urgent assessment. A mild ache that you can link to exercise, gas or constipation, and that improves within a day or two, is rarely serious.

Right side pain: causes and what is different

The right side holds organs that the left side does not, so the list differs.

• Upper right: the liver and gallbladder. Gallstones cause attacks of pain under the right ribs, often after a fatty meal, sometimes spreading to the right shoulder blade. Hepatitis causes a dull ache with tiredness and sometimes yellow skin.
• Lower right: the appendix. Appendicitis classically starts as a vague ache around the belly button, then settles in the lower right within 12 to 24 hours. Walking, coughing and bumps in the car make it worse.
• Either side: kidney stones, kidney infection, ovarian problems, hernias, constipation and muscle strain affect both sides equally.

Side pain with other symptoms

• Back and side pain together: suggests the kidney (stones, infection) or the spine and back muscles. Kidney pain is deep and steady or wave-like. Spinal pain changes with posture. See back pain.
• Painful urination or blood in urine: points to a urinary infection or stone. See painful urination and blood in urine.
• Fever: suggests infection or inflammation, such as kidney infection, appendicitis, diverticulitis or pneumonia.
• Nausea and vomiting: common with stones, appendicitis, gallbladder attacks, pancreatitis and ovarian torsion.
• Diarrhea or constipation: suggests a bowel cause.
• Pain with breathing: suggests the chest wall, lung lining or ribs. See rib pain.
• A rash in a band: shingles.

How doctors find the cause

A clinician will ask where the pain started and where it moves to, how quickly it came on, whether it comes in waves, what makes it worse, and about fever, urine, bowel habits, your menstrual cycle and the chance of pregnancy. They will press gently on your belly and tap over the kidneys.

Common tests:

• Urine test: checks for infection and blood, which suggests a stone.
• Pregnancy test: for anyone who could be pregnant.
• Blood tests: a blood count and CRP for infection, kidney and liver function, and lipase for pancreatitis.
• Ultrasound: good for the gallbladder, ovaries and kidneys, and in pregnancy and children.
• CT scan: the main test for kidney stones, appendicitis and diverticulitis in adults.

Side pain treatment and home care

Treatment depends on the cause. For mild pain that you can link to a muscle strain, gas or constipation:

• Muscle strain: rest from the activity that caused it for a few days, then gentle movement. Use a heat pack or a cold pack wrapped in a cloth. Acetaminophen (paracetamol) or ibuprofen can help. Follow the label dose. Avoid NSAIDs if you have kidney disease, stomach ulcers or take blood thinners.
• Side stitch: slow down, breathe deeply and press on the painful spot. Avoid large meals and sugary drinks for 2 hours before exercise.
• Gas and constipation: drink more water, add fiber gradually, walk after meals, and use an over-the-counter laxative briefly if needed.

Do not take pain relievers to mask pain that is severe or getting worse, especially in the lower right side, before you are examined. Medical treatments include antibiotics for kidney infection or diverticulitis, pain relief and medicines that help stones pass, and surgery for appendicitis, ovarian torsion or ectopic pregnancy.

Frequently asked questions

When should I worry about left side pain?

Get same-day care if the pain is severe, keeps getting worse, or comes with fever, vomiting, blood in your urine or stool, a hard swollen belly, or dizziness. Call 911 or your local emergency number for sudden severe pain with fainting, chest pain or breathlessness. Mild pain linked to exercise, gas or constipation that improves within a day or two is rarely serious.

What causes pain in my side?

The most common causes are muscle strain, a side stitch, trapped gas and constipation. Kidney stones and kidney infections cause pain in the back of the side. Appendicitis and gallstones cause right-sided pain, and diverticulitis usually causes lower left pain. In women, ovarian cysts and ectopic pregnancy are important causes on either side.

What does kidney pain in the side feel like?

Kidney pain is deep, below the ribs in the back of the side, and does not change when you move or press on the muscles. A stone causes waves of intense pain that may spread to the groin, often with nausea. An infection causes a steadier ache with fever and urinary symptoms.

How can I tell if side pain is a muscle strain?

Muscle pain usually follows lifting, twisting, sport or heavy coughing. It is sore when you press on the spot and hurts when you bend, twist or breathe deeply, but eases with rest. You feel otherwise well, with no fever, vomiting or urine changes. It usually improves within a few days to two weeks.

What causes a side ache when running?

A side stitch is a sharp or cramping pain just under the ribs during exercise. It may come from irritation of the lining of the belly or strain on the diaphragm. It is more common after eating or drinking before exercise and settles within minutes of stopping. It is harmless.

Can gas cause sharp pain in the side?

Yes. Gas trapped where the colon bends, under the left or right ribs, can cause sharp, stabbing pain that moves around and eases when you pass gas or have a bowel movement. Gas pain does not cause fever or vomiting, so those symptoms need a medical check.