Pain in your lower left side most commonly comes from your colon, particularly from diverticulitis or constipation, but it can also involve your kidneys, muscles, or reproductive organs depending on your sex. The cause ranges from something temporary and harmless to conditions that need prompt treatment, so understanding what else you’re feeling alongside the pain is the fastest way to narrow it down.
Diverticulitis: The Most Common Culprit
Your lower left abdomen is home to the sigmoid colon, the last stretch of your large intestine before it reaches the rectum. Small pouches can form along this section of the colon wall over time, and when one of those pouches becomes inflamed or infected, the result is diverticulitis. It’s the single most common diagnosis behind lower left abdominal pain in adults, especially over age 40. Rates of acute diverticulitis in people aged 40 to 49 increased by 132% between 1980 and 2007, and cases are climbing in younger adults too.
Diverticulitis typically causes a steady, aching pain that builds over a day or two rather than hitting all at once. You may also notice fever, nausea, or a change in bowel habits like constipation or diarrhea. The pain tends to worsen with movement or pressure on the area. Diagnosis usually involves a CT scan and blood work to check for signs of infection.
Constipation and Other Bowel Causes
Before jumping to more serious possibilities, consider the simplest one: constipation. Stool backs up most often in the sigmoid colon, which sits right in your lower left abdomen. The pain is usually crampy and comes with bloating, a feeling of fullness, and difficulty passing stool. It tends to ease once you have a bowel movement.
Other bowel-related causes include inflammatory bowel disease (such as Crohn’s disease or ulcerative colitis), which produces recurring episodes of cramping, diarrhea, and sometimes bloody stool. Infectious colitis from a stomach bug can cause similar symptoms but usually passes within days. A less common possibility is reduced blood flow to part of the colon, which causes sudden pain and is more likely in older adults with heart disease or circulation problems.
Kidney Stones
A stone forming in or passing through your left kidney can cause pain that starts in your side and back below the ribs, then radiates down toward your lower abdomen and groin. This pain is distinctive: it comes in intense waves, shifts location as the stone moves through your urinary tract, and is often described as one of the worst pains people have experienced. You can’t get comfortable no matter what position you try.
Alongside the pain, kidney stones frequently cause a burning sensation when you urinate, pink or red-tinged urine, cloudy or foul-smelling urine, and a persistent urge to urinate even when little comes out. Nausea and vomiting are common. If fever and chills develop on top of the pain, that suggests the stone has caused an infection, which needs treatment quickly.
Causes Specific to Women
Several reproductive conditions cause pain that localizes to one side of the lower abdomen.
Ovarian cysts are fluid-filled sacs that form on or in an ovary. Most are small, cause no symptoms, and resolve on their own within a few menstrual cycles. A larger cyst, though, can produce a dull ache or sharp pain on one side below your bellybutton, along with bloating and a sensation of fullness or pressure. If a cyst ruptures or twists, the pain becomes sudden and severe, sometimes accompanied by fever, vomiting, rapid breathing, or lightheadedness.
Endometriosis occurs when tissue similar to the uterine lining grows outside the uterus. The hallmark is pelvic pain that’s far worse than typical menstrual cramping, often bad enough to keep you from work or daily activities. The pain usually tracks with your cycle, starting before your period and extending beyond it, but it can also occur outside your period entirely. Lower back pain, pain during sex, pain with bowel movements, bloating, fatigue, and nausea are all common. If your lower left pain seems to flare and fade with your menstrual cycle, endometriosis is worth investigating.
Ectopic pregnancy is a time-sensitive emergency. If a fertilized egg implants outside the uterus, typically in a fallopian tube, it causes lower abdominal pain on one side along with vaginal bleeding or spotting, back pain, shoulder tip pain, nausea, and feeling faint. If there’s any chance you could be pregnant and you’re experiencing these symptoms, this needs immediate evaluation.
Causes Specific to Men
An inguinal hernia develops when tissue, usually part of the intestine, pushes through a weak spot in the abdominal wall near the groin. The telltale sign is a visible or palpable bulge on one side of the pubic bone that becomes more obvious when you stand up, cough, or strain. The area around the bulge often burns or aches, and you may feel pain or pressure in the groin when bending over, coughing, or lifting. In some cases the protruding tissue descends into the scrotum, causing pain and swelling around the testicles. The bulge is usually something you can feel with your hand when standing.
Prostatitis, an inflammation of the prostate gland, and urinary tract infections can also cause lower abdominal discomfort in men, often accompanied by urinary symptoms like burning, frequency, or difficulty urinating.
Muscle and Soft Tissue Pain
Not all lower left pain originates from an organ. The psoas muscle, a deep core muscle that connects your lower spine to your hip, runs through the lower abdomen and can mimic internal pain when strained or inflamed. Psoas-related pain tends to worsen with specific movements: standing up straight, walking, or lifting your leg. It may radiate down your leg, and in severe cases it can make you limp or shuffle your feet. If the pain started after exercise, heavy lifting, or a sudden movement, a muscular cause is likely.
Abdominal wall injuries, including small tears or hematomas in the muscle itself, can also create localized pain that worsens when you tense your core, like during a sit-up or when rolling over in bed. A useful test: if pressing on the tender spot while flexing your abdominal muscles makes the pain worse, it’s more likely coming from the wall rather than inside the abdomen.
How to Tell What’s Serious
Mild, intermittent pain that comes and goes over a few days, especially if it’s tied to diet, bowel habits, or physical activity, is often something you can monitor. But certain combinations of symptoms signal that you need urgent care:
- Sudden, severe pain that comes on within minutes, especially if you feel faint or lightheaded
- Pain with fever and chills, which suggests infection
- Blood in your stool or urine, or stool that is black and tarry
- Vomiting blood or vomit that looks like coffee grounds
- Pain so intense you cannot sit still or find a comfortable position
- Pain with vaginal bleeding if there’s any possibility of pregnancy
Abdominal pain that steadily worsens over hours rather than easing on its own also warrants prompt evaluation, even if none of the above red flags are present. A worsening trajectory matters more than how bad the pain is at any single moment.