Penis anatomy: a complete guide

Most people know the basic external shape, but not necessarily the names of the individual parts or what's actually happening inside during an erection — and sensitivity in particular is a lot less evenly distributed than the general shape suggests.

External anatomy

• Glans — the head; typically the most visually distinct and one of the more sensitive areas.
• Corona — the ridge where the glans meets the shaft, commonly reported as highly sensitive.
• Frenulum — a band of skin on the underside connecting the glans to the shaft (or to the foreskin, if present); often the single most sensitive point.
• Shaft — the main length of the penis.
• Foreskin — a retractable fold of skin covering the glans in uncircumcised penises; absent in circumcised ones. See our guide to smegma for foreskin-specific hygiene.
• Urethral opening — at the tip of the glans, where both urine and ejaculate exit (at different times, controlled by separate mechanisms).

What's happening internally

Two parallel chambers called the corpora cavernosa run along the top and sides of the shaft, and a third chamber, the corpus spongiosum, surrounds the urethra and extends into the glans. During arousal, blood flow into these chambers increases while the veins that normally drain blood out constrict — the combination is what produces and sustains an erection. The corpus spongiosum stays comparatively softer than the corpora cavernosa even during a full erection, which is a structural necessity: if it engorged as firmly as the other two, it would compress the urethra shut. See our full guide to erections for how firmness naturally fluctuates, and our guide to ejaculation for what happens after.

Sensitivity isn't evenly distributed

The frenulum and corona are the areas most commonly reported as most sensitive, though individual variation is significant — what's most sensitive for one person may not be for another, and sensitivity can shift depending on arousal level. Direct glans stimulation, especially immediately after orgasm, is uncomfortable or overstimulating for a lot of people; that's a normal refractory response tied to the refractory period, not a problem with the anatomy.

Foreskin, if present

The foreskin is a natural, functional structure that covers and protects the glans when not retracted. It should generally retract fully in adulthood; a foreskin that's difficult or painful to retract can indicate phimosis, a real medical condition worth a doctor's visit rather than working around on your own. See our smegma guide for day-to-day hygiene, and our medical disclaimer for when anatomy questions belong with a clinician instead of an article.

Size variation is normal

A frequently-cited 2015 systematic review by Veale and colleagues, pooling data on over 15,000 men, found an average erect length of roughly 13.1 cm — but the point of a systematic review like that is the range around the average, not the average itself. Natural variation is wide, and size outside of specific functional concerns (pain, difficulty with certain positions) generally isn't something to be concerned about on its own. Curvature is also normal, lifelong variation for a lot of men — a new or worsening curve is a different question, covered in our guide to Peyronie's disease.