Letter F
Flank pain
Also known as: Side pain, Loin pain
Flank pain symptom guide: what it can mean, possible causes, and when to seek care. Educational only.
Overview
Pain in the flank (side of the lower back) can come from muscle strain, injury, or inflammation. Flank pain may relate to the kidney or muscles. This is general information only, not a diagnosis. Severe, sudden, or fever-related pain needs professional assessment.
Possible causes
- Muscle strain or posture
- Injury or overuse
- Joint inflammation
- Infection (less often)
- Kidney stones
- Urinary tract infection
When to see a doctor
See a clinic if flank (side of the lower back) pain is severe, limits activity, lasts a week, or comes with swelling/fever.