April 18, 2007

Q&A: The Science Behind Erections and Flaccid Penis Size

A male reader asks why his penis size varies while flaccid, he wonders if this is normal.

Print More

Question: My penis size when flaccid varies from about 1.5″ to 3.5″. Is this normal? I understand that sizes vary, but why does it shrink and grow like it does? I’m 18 years old and average height and weight. Please let me know what you think. Thanks.

Yes, it is common for men to notice different sizes of their flaccid (soft).

Penile Hardness A Continuum

However, rather than thinking of one’s penis as either flaccid (soft) or erect (hard), it is probably more accurate to think of penile hardness (or softness) as lying on a continuum, which some researchers conceptualize as degrees or erectile “density” or “rigidity”.

For example, you may have had erections that you thought were quite hard. Alternatively, you may have had erections that seemed only somewhat hard and that perhaps required more stimulation (either physically or through fantasy) in order to ejaculate or experience orgasm.

The Science Behind Erections

Let’s look at the science behind erections and then consider how this relates to your experience. P

enises become more erect or rigid when more blood flows into the penis than the amount that flows out. As blood flow builds inside the chambers of the penis, pressure also builds, and this pressure is what is often translates into a penis being described as “hard”.

The process by which the body allows more blood to flow into the penis than out is complex. A man may experience physical stimulation or mental stimulation (as through feelings of sexual arousal, excitement or fantasy).

This stimulation can activate various nerves in the body and the release of certain neurotransmitters. These physical changes are responsible for the relaxation of smooth muscle in the penis (this smooth muscle is under “involuntary” control, meaning you can’t make yourself relax or contract these muscles). The relaxation of this smooth muscle allows for more blood to fill the penis – and quite quickly.

Men can voluntarily contract other muscles that are at the base of their penis (the muscles that make a penis appear to “bounce” or “dance”, as some call it). By contracting these muscles, men may be able to make their erections even more rigid (or “hard”) as the contraction may compress the base of certain blood-filled chambers in the penis and thus increase pressure or rigidity.

Sexual and Non-Sexual Stimulation

Variations in blood flow or muscular contraction (or relaxation) can therefore affect the size of a penis. Different degrees of stimulation may allow different amounts of blood to flow into the penis, and we’re not just referring to sexual stimulation.

Sometimes men find that non-sexual physical stimulation (such as the friction of one’s penis against the bed while sleeping, or against loose-fitting clothes like boxers) might be enough to cause a slight increase in penile size.

Flaccid Penis Size and Temperature Changes

Men also often describe changes in their flaccid penis size based on outside temperatures (usually, that their flaccid penis seems smaller in water that is cooler than their body temperature, such as after a shower or a swim).

Then again, they may find it easier to become erect in warmer water, such as in a hot tub.