This is very helpful. Now I have a precise picture. Here's the refined answer based on your exact location:
Pain at the Lower Left Breast / Where Breast Meets Abdomen
This specific location - straight down from the nipple, at the lower border where the breast tissue meets the upper abdomen - is the inframammary / subcostal region. This changes the differential significantly.
#1 Most Likely: Slipping Rib Syndrome
This fits your location almost perfectly. The lower ribs (8th, 9th, 10th) are "false ribs" - they don't attach directly to the sternum and are held together by cartilage and fibrous tissue. When those attachments weaken or tear:
- The rib edge slips behind the one above it whenever you contract your abdominal muscles - which happens when you laugh, smile, cough, or twist
- This causes a sudden, sharp, lancinating (stabbing) pain right in the subcostal/lower chest area
- Often accompanied by a clicking or popping sensation
- Pain is in the lower chest / upper abdomen junction - exactly where you feel it
- Unilateral (one side only, commonly the left)
"SRS ordinarily causes unilateral sharp, often lancinating pain in the subcostal region. The syndrome is associated with hypermobility of the costal cartilage... with slipping of the affected rib behind the superior adjacent rib during contraction of the abdominal musculature." - Sleisenger & Fordtran's Gastrointestinal and Liver Disease
How to confirm it: A doctor can do the "hooking maneuver" - fingers hooked under your lowest rib and gently pulled forward. If it reproduces your pain (and sometimes a click), that confirms the diagnosis.
Treatment: Usually conservative - anti-inflammatory meds, activity modification, avoiding movements that trigger it. Occasionally a nerve block or surgical rib excision is needed for persistent cases.
#2 Intercostal Nerve Irritation / Lower Costal Chondritis
The cartilage at the lower rib junctions (5th-8th ribs) can become inflamed or irritated:
- Sharp pain at the inframammary crease
- Worsens with any muscle contraction in the area (laughing strongly engages these muscles)
- Tender to touch along the lower rib margin
#3 Diaphragmatic / Referred Splenic Pain
The upper-left abdomen (splenic flexure of the colon, spleen, stomach fundus) sits right under this area. Sometimes:
- Splenic flexure syndrome - trapped gas in the left colon causes sharp referred pain upward into the lower left chest/breast area
- Gastric distension - a full or gassy stomach can press upward
- Both are worsened by movement and laughing (increased abdominal pressure)
#4 Precordial Catch Syndrome
Still possible - classically described as pain "right under the left nipple," which matches your described location. Brief, sharp, seconds-to-minutes, benign.
Quick Self-Check
Press firmly along the lower edge of your left rib cage (the curved bony border where your breast meets your abdomen). If it reproduces the pain exactly, this is strongly musculoskeletal - most likely slipping rib syndrome or lower costochondritis.
Bottom Line
Given your exact location (lower breast / inframammary / where breast meets abdomen) + sharp pain worsened by laughing (abdominal muscle contraction), Slipping Rib Syndrome is the top suspect. It is benign but can be quite painful and recurrent. A doctor can confirm it with a simple physical exam maneuver.
No cardiac cause produces this pattern at this location worsened specifically by smiling/laughing.
Disclaimer: This is educational information only. Please see a doctor for proper evaluation, especially if the pain is recurring, severe, or accompanied by other symptoms.