The difference between a “grower” and a “shower” comes down to how much the penis changes in length between its flaccid and erect states. A clinical study that put actual numbers to the distinction found that about three-quarters of men are showers, meaning their penis stays relatively close to its erect size even when soft, while roughly one in four are growers who see a more dramatic expansion. The reasons span connective tissue elasticity, smooth muscle tone, vascular mechanics, and age, all of which interact in ways that make the flaccid state far more variable than the erect one.
How Clinicians Define the Difference
The terms “grower” and “shower” started as slang, but a 2018 clinical study of 278 men formalized a cutoff. Researchers measured penile length in both the flaccid and fully erect states and used the median gain as a dividing line: men whose penis grew by four centimeters or more were classified as growers, and those below that threshold as showers. By that definition, 26% qualified as growers, with an average gain of about five centimeters, while the remaining 74% were showers, gaining about three centimeters on average.1PubMed. Grower or shower? Predictors of change in penile length from the flaccid to erect state It is worth noting that the study’s participants were men being evaluated for erectile dysfunction, so whether those percentages hold in the broader population remains an open question. Still, it is the most cited clinical benchmark for the grower-shower distinction.
The four-centimeter cutoff is somewhat arbitrary, and there is no sharp biological boundary between the two categories. Penile expansion exists on a continuous spectrum. Some men gain barely any length, others double their flaccid measurement, and most land somewhere in between. The labels are a useful shorthand, not a diagnosis.
Why the Flaccid Penis Is So Variable
Erect length is surprisingly consistent from one measurement to the next. Flaccid length is not. That asymmetry is the core of why growers and showers exist: the flaccid state is actively maintained by the nervous system and is sensitive to a wide range of influences, while erection is a more uniform hydraulic event.
When the penis is soft, the sympathetic nervous system keeps the smooth muscle inside the erectile chambers contracted. Noradrenaline released by sympathetic nerves constricts both the arteries feeding the penis and the smooth muscle lining the internal spongy tissue, restricting blood flow and keeping volume low.2International Journal of Impotence Research. Physiological regulation of penile arteries and veins How tightly that smooth muscle contracts at rest varies between individuals. A man whose baseline sympathetic tone runs high, or whose smooth muscle is particularly responsive to noradrenaline, will tend to have a smaller flaccid penis relative to his erect size. He is a grower. A man whose resting tone is lower, letting more blood pool in the erectile tissue even when soft, will appear closer to his erect size. He is a shower.
Cold temperatures, stress, anxiety, and physical exertion all ramp up sympathetic activity and temporarily shrink the flaccid penis. This is why the same man can look like a shower after a warm bath and a grower after a cold swim. The erect state, by contrast, is driven by a strong parasympathetic signal that overrides resting tone and dilates arteries to fill the erectile chambers almost completely regardless of starting conditions.
The Role of Connective Tissue and Elasticity
The penis is wrapped in a tough, fibrous sheath called the tunica albuginea. This tissue has a layered structure of collagen and elastic fibers that gives the organ both rigidity during erection and flexibility when soft.3The Journal of Urology. The Anatomy of the Tunica Albuginea in the Normal Penis and Peyronie’s Disease The ratio of elastic fibers to collagen in this sheath matters. More elastic fiber means the tissue can stretch further during erection and retract more completely when soft, producing a bigger difference between the two states. More collagen relative to elastin means less retraction, so the flaccid penis stays closer to its erect length.
This tissue composition varies from person to person and is probably influenced by genetics, though the specific genes involved are still poorly mapped. We know that collagen genes like COL1A1 and COL6A1 play roles in penile connective tissue, but research so far has focused on abnormalities like penile curvature rather than normal variation in elasticity.4PubMed Central. The impact of COL1A1 and COL6A1 expression on hypospadias and penile curvature severity Nobody has yet identified a “grower gene” or a “shower gene,” and given the number of tissue types involved, the answer is almost certainly polygenic, meaning many genes each contribute a small effect.
Age Is the Strongest Known Predictor
In the 2018 study, when researchers controlled for factors like height, weight, and medical history, only one variable reliably predicted whether a man was a grower: younger age.1PubMed. Grower or shower? Predictors of change in penile length from the flaccid to erect state Younger men were significantly more likely to be growers than older men. The mechanism behind this tracks with what we know about aging tissue.
As men age, the elastic fibers in the tunica albuginea and the smooth muscle lining the erectile chambers are gradually replaced by collagen. The tissue becomes stiffer and less compliant.5PubMed Central. The aging penis: what is it trying to tell us? At the same time, atherosclerosis in the small arteries feeding the penis reduces the hydraulic efficiency of erection. The net effect is a double shift: the flaccid penis retracts less because the tissue is stiffer, and erection may not reach its former peak because blood flow is reduced. Both changes push a man toward the shower end of the spectrum, not because his erect size has grown, but because his flaccid size has crept upward while his erect size may have slightly declined.
Research on the tunica specifically has found that elastic fiber concentration drops with age and is even lower in men with erectile dysfunction.6PubMed. Structural alterations in the tunica albuginea of the penis: impact of Peyronie’s disease, ageing and impotence So the grower-shower classification is not necessarily a fixed trait for life. A man who was a grower at 25 may gradually shift toward shower territory as his connective tissue changes with age.
Can You Predict Erect Size from Flaccid Size?
One of the most practical implications of the grower-shower distinction is that flaccid size is a poor predictor of erect size. This is not just folk wisdom; measurement studies back it up. A large, multi-center study found that flaccid measurements underestimated erect length by roughly 20% on average, and the discrepancy varied significantly depending on who was doing the measuring.7International Journal of Impotence Research. Outcomes of variation in technique and variation in accuracy of measurement in penile length measurement For growers, the underestimate would be even larger.
A more reliable proxy turns out to be the stretched flaccid length, where the soft penis is gently pulled to its maximum extension. Engineering analysis has shown that this measurement closely approximates erect length, though clinicians in practice often do not apply enough force to reach the full stretch, requiring about 450 grams of tension to match erection length.8International Journal of Impotence Research. Predicting penile size during erection The stretched measurement largely neutralizes the grower-shower variable because it mechanically extends the elastic tissue to its near-maximum, mimicking what blood pressure achieves during erection. A systematic review that compiled data from over 15,000 men found that mean stretched length and mean erect length were almost identical, at about 13.2 and 13.1 centimeters respectively.9PubMed. Am I normal? A systematic review and construction of nomograms for flaccid and erect penis length and circumference in up to 15,521 men
This equivalence is clinically useful. Urologists who need to assess penile length, whether before surgery or for evaluating a patient’s concerns, generally prefer the stretched measurement precisely because the flaccid state is too unreliable.
Body Size Does Not Predict Penile Size
A persistent assumption is that taller or larger men will have larger penises. Research on men under 40 found no meaningful correlation between penile dimensions and height, weight, body mass index, or waist-to-hip ratio.10Urology. Size of external genital organs and somatometric parameters among physically normal men younger than 40 years old This also means that body size does not predict whether someone is a grower or a shower. A tall, muscular man and a short, lean man could easily have the same erect length but very different flaccid presentations.
There is one indirect body-size effect worth noting. Excess fat in the pubic area can bury the base of the penis, making the visible flaccid length appear shorter without changing the actual tissue dimensions. This is sometimes called a “buried penis” in clinical contexts. The measurement studies referenced above found that measuring from the pubic bone to the tip of the glans, pressing the ruler into the fat pad, produced more reliable and observer-independent readings, especially in overweight patients.7International Journal of Impotence Research. Outcomes of variation in technique and variation in accuracy of measurement in penile length measurement So weight gain can make a man appear more like a grower without any actual change in his penile tissue.
What Blood Flow Has to Do with It
Erection is fundamentally a vascular event. Arteries dilate, blood floods the spongy chambers inside the penis, and the expanding tissue compresses the veins against the tunica albuginea, trapping the blood and producing rigidity. Research on the hemodynamics of this process has shown that nerve-stimulated erection depends on a large increase in total arterial inflow, while pharmacologically induced erection relies more on internal rerouting of blood already present in the tissue.11The Journal of Urology. Hemodynamics of Penile Erection: III. Measurement of Deep Intracavernosal and Subtunical Blood Flow and Oxygen Tension
For growers specifically, the vascular expansion is dramatic because their resting state involves strong arterial constriction and minimal blood volume. Their smooth muscle has to relax substantially, their arteries have to open wide, and a large volume of blood must rush in to achieve full size. For showers, the resting state already features relatively relaxed smooth muscle and more baseline blood flow, so the hydraulic change needed during erection is smaller. This tracks with the oxygenation data: cavernosal tissue sees significant increases in oxygen even at low levels of engorgement, suggesting that even partial filling substantially changes the tissue environment.12PubMed. The correlation between intracavernosal pressure and cavernosal blood oxygenation
Conditions That Shift the Balance
Certain medical conditions can alter a man’s position on the grower-shower spectrum. Peyronie’s disease, a fibrotic condition where scar tissue forms in the tunica albuginea, reduces the tissue’s ability to stretch during erection. The scarring can cause curvature, narrowing, and shortening of the erect penis.13PubMed Central. Surgery for Peyronie’s disease Because the fibrosis replaces elastic tissue with rigid collagen, it also tends to reduce the difference between flaccid and erect length, pushing affected men toward the shower category, though not in a way anyone would welcome since both function and erect size are compromised.
Pelvic surgery can also temporarily change the equation. A long-term study of men who underwent radical prostatectomy found that stretched penile length decreased by an average of one centimeter at three months post-surgery, with the reduction persisting for about two years before gradually recovering to near-baseline by four to five years.14PubMed. The natural history of penile length after radical prostatectomy: a long-term prospective study Nerve damage during surgery and the period of disuse that follows likely contribute to smooth muscle atrophy and temporary loss of elastic capacity, though the eventual recovery suggests the tissue can remodel given enough time.
Hormonal Influences During Development
Testosterone during puberty drives penile growth, and it is natural to wonder whether differences in hormonal exposure explain why some men end up as growers and others as showers. The evidence here is thin but suggestive. A study of boys who experienced early testosterone exposure, either through precocious puberty or congenital adrenal hyperplasia, found that their adult penile length fell within the normal range. Early androgen exposure caused the penis to grow during childhood, but it did not result in a smaller or larger final adult size than expected.15The Journal of Urology. The Effect of Prepubertal Androgen Exposure on Adult Penile Length This suggests that the endpoint of growth is robustly programmed and that final erect size is not easily nudged by variations in timing of testosterone exposure.
What hormones might influence, though, is the composition of the tissue rather than the final length. Testosterone and its metabolite dihydrotestosterone affect smooth muscle density, collagen deposition, and elastic fiber maintenance in the penis. Differences in androgen receptor sensitivity or local hormone metabolism could plausibly lead to different ratios of elastic to collagenous tissue in the tunica, which as discussed above is a major determinant of how much the penis retracts when soft. This remains speculative; no study has directly tested whether androgen receptor variants correlate with grower or shower status.
The Perception Problem
A 2025 clinical study on penile self-assessment found that men consistently misjudge their own dimensions, with the perception bias differing between the flaccid and erect states. The same study noted that while the 2018 grower-shower classification found no clinically significant differences in sexual function between the two groups, there may be psychosexual effects that warrant further study.16Sexual Medicine. Visual illusion in male self-assessment of penile dimensions: a clinical study on penile length perception bias between flaccid and erect states In plain terms: being a grower does not affect how well the penis works, but it may affect how a man feels about it.
The foreshortening effect of looking down at one’s own body exaggerates the apparent smallness of the flaccid penis. Growers, who start from a smaller baseline when soft, may be especially prone to underestimating their size. In locker rooms, communal showers, and other settings where flaccid comparisons happen, growers are at a visual disadvantage despite having no functional or erect-size difference. This mismatch between what a man sees when he looks down and what actually happens during sex is a well-recognized source of unnecessary anxiety.
Sexual Selection and Why Flaccid Display May Have Mattered
Humans are unusual among primates in having a relatively large, pendulous penis that is visible even when flaccid. Some evolutionary researchers have asked whether this conspicuous display served a signaling function. An experimental study using digitally manipulated male body images found consistent directional selection favoring taller men with a more V-shaped torso and a larger penis, with both female raters and male raters assessing rivals with larger penises as more sexually competitive and physically threatening.17PLOS Biology. Experimental evidence that penis size, height, and body shape influence assessment of male sexual attractiveness and fighting ability in humans The authors concluded that both female mate choice and male-male competition likely contributed to the evolution of larger penile size in humans.
If flaccid display was part of the selective pressure, then being a shower, with a penis that appears large even at rest, could have carried a social advantage in ancestral environments where clothing was minimal. That said, evolutionary speculation about genital morphology is notoriously difficult to test, and the trait’s persistence in both grower and shower forms suggests neither is strongly disadvantaged. The two phenotypes may simply reflect natural variation in the balance between retractile efficiency and resting display, maintained by the many genes and tissue properties that underlie penile anatomy.