Clinical pH Reference
pH Atlas
A community-friendly map of pH across the human body — one spectrum, plain-language explanations, and an interactive checker for a measured reading.
Arterial norm:
7.35–7.45
Full range · pH 0–14
02468101214
Near-neutral zone, zoomed · pH 6.5–9.0
Most internal fluids cluster tightly here — too close to separate on the full scale above.
6.57.07.58.08.59.0
Reproductive tract, mapped
One of the steepest pH gradients in the body: acidic at the vaginal opening, alkaline by the upper uterine cavity.
- Vaginal pH 3.8–4.5 (normal) — maintained by lactobacilli; >4.5 points toward bacterial vaginosis or trichomoniasis. Yeast (candida) infections often occur at a normal-to-slightly-low pH, so pH alone does not rule a yeast infection in or out.
- Cervical mucus pH ~6.4–8.0 — shifts more alkaline near ovulation (its most sperm-friendly window sits roughly 7.0–8.5) and more acidic afterward.
- Uterine cavity pH ~7.5–7.8 — the alkaline endpoint of the gradient; helps sperm capacitation once they clear the cervix.
- Semen pH ~7.2–8.0 — the WHO reference band; persistently <7.2 raises questions about seminal-vesicle contribution, while several studies find healthy fertile samples running higher than this range.
Cardiovascular tissue
Arterial blood is the whole-body signal; heart muscle itself has its own tightly regulated internal pH.
- Myocardial (heart muscle) intracellular pH ~7.2 at rest — similar to most other cells.
- During ischemia, restricted blood flow lets acid metabolites accumulate and intracellular pH can fall toward ~6.5, with an even larger drop just outside the cell.
- This drop is used experimentally and intraoperatively as a marker of inadequate perfusion — it is not something measured at home or in routine bloodwork.
System-by-system panel
| System | Site | Typical pH | Zone |
|---|---|---|---|
| Digestive | Stomach | 1.5–3.5 | Strong acid |
| Digestive | Small intestine | 7.5–8.0 | Alkaline |
| Digestive | Colon | 5.5–7.0 | Mild acid |
| Circulatory | Arterial blood | 7.35–7.45 | Tightly held |
| Circulatory | Myocardial tissue (ischemic) | ~6.5–7.0 | Acidotic shift |
| Nervous | Cerebrospinal fluid | 7.3–7.5 | Near-neutral |
| Integumentary | Skin surface | 4.7–5.7 | Mild acid |
| Renal | Urine | 4.5–8.0 | Wide range |
| Reproductive | Vaginal | 3.8–4.5 | Acidic |
| Reproductive | Cervical mucus | 6.4–8.0 | Cycle-dependent |
| Reproductive | Uterine cavity | 7.5–7.8 | Alkaline |
| Reproductive | Semen | 7.2–8.0 | Alkaline |
Key takeaways
- Blood is held in the narrowest band of any fluid in the body — a swing of a few tenths is a medical emergency.
- Stomach acid is deliberately extreme, built for digestion and pathogen control.
- Skin stays mildly acidic to protect the barrier and its resident microbiome.
- Intestinal and pancreatic fluids run alkaline to activate digestive enzymes.
- The reproductive tract runs its own gradient from acidic (vaginal, pathogen defense) to alkaline (uterine, sperm support) within a few centimeters.