Erections are possible without testes, because the core mechanism behind an erection is vascular and neurological rather than purely hormonal. The testes are the body’s main testosterone factory, and losing them does change sexual function in meaningful ways, but the physical hardware that produces an erection can still work. How well it works, and for how long, depends on factors like remaining androgen sources, the type of erotic stimulus involved, and whether medical support is used.
How Erections Actually Work
An erection is fundamentally a blood-flow event. When a man becomes aroused, nerve signals trigger the release of nitric oxide in the erectile tissue of the penis. Nitric oxide relaxes the smooth muscle inside the corpora cavernosa, the two sponge-like chambers that run the length of the shaft. As that smooth muscle relaxes, blood rushes in and fills the chambers, and the expanding tissue compresses the veins that would normally drain blood away. The result is rigidity.1Europe PMC. The role of nitric oxide in erectile dysfunction: implications for medical therapy
Testosterone contributes to this process, but it does not single-handedly drive it. Androgens help maintain the health of the smooth muscle tissue, support nitric oxide production, and play a role in sexual desire. Remove testosterone entirely, and erections become harder to achieve and sustain over time. But the nerve pathways, blood vessels, and smooth muscle that make erections physically possible remain in place. This distinction is critical for understanding what happens after the testes are removed.
Two Separate Pathways to Erection
The nervous system has more than one route to trigger an erection, and these pathways differ in how much they depend on testosterone. Reflexogenic erections happen through a spinal reflex arc: direct physical stimulation of the genitals sends signals to the sacral spinal cord, which fires back signals that dilate blood vessels in the penis. This loop can function even without input from the brain, which is why men with certain spinal cord injuries above the sacral level can still get erections from touch.2Physiology & Behavior. Neural control of erection
Psychogenic erections, on the other hand, originate in the brain. Fantasy, visual stimulation, or emotional arousal sends descending signals down the spinal cord to the erectile tissue. Both pathways converge on the same vascular endpoint, but they rely on different neural circuits to get there. The reflexogenic pathway is relatively hormone-independent, meaning it can continue to function even in very low testosterone states. The psychogenic pathway is more nuanced: while desire and spontaneous arousal are clearly affected by testosterone levels, the actual erectile response to visual erotic stimuli turns out to be surprisingly resilient.
What Happens to Erections in Low-Testosterone States
Some of the most telling evidence comes from studies of men with severe hypogonadism, a condition where the body produces very little testosterone. Researchers compared hypogonadal men with healthy controls and found a striking split. During sleep, hypogonadal men had substantially fewer and weaker erections, both in terms of how much the penis expanded and how rigid it became. But when the same men watched erotic visual material while awake, their erectile responses were similar to those of healthy controls.3PubMed. The effects of testosterone replacement on nocturnal penile tumescence and rigidity and erectile response to visual erotic stimuli in hypogonadal men
This finding has been replicated and discussed extensively. Nocturnal erections, which happen during REM sleep and serve partly as a maintenance function for penile tissue, are clearly androgen-dependent. But the waking erectile response to erotic stimuli appears to rely on a system that is largely androgen-independent, even though desire and motivation to seek out those stimuli may be reduced.4The Journal of Sexual Medicine. Testosterone and Sleep‐Related Erections: An Overview
In practical terms, a man without testes who receives adequate physical stimulation or views arousing material may still achieve some degree of erection, even without testosterone replacement. The spontaneous erections that healthy men experience throughout the day and night, however, are likely to diminish or disappear.
The Adrenal Backup System
Removing the testes does not eliminate every source of androgens in the body. The adrenal glands, which sit on top of the kidneys, produce androgen precursors, molecules that can be converted into small amounts of active testosterone and related hormones in peripheral tissues. In younger men especially, this adrenal contribution means that complete androgen deprivation after castration may not actually occur.5Oxford Academic. Are Androgens Critical for Penile Erections in Humans? Examining the Clinical and Preclinical Evidence
This is an important difference between humans and the rodent models often used in research. Rats’ adrenal glands do not produce androgens, so castration in a rat creates near-total androgen elimination. In humans, the adrenal contribution is modest compared to testicular production, but it is not zero. It may help explain why some men who have lost their testes retain more erectile function than animal studies would predict, particularly in the years immediately following surgery.
What History Tells Us About Castrated Men
The question of sexual function after castration is not new. For thousands of years, various cultures practiced castration for political, religious, or musical purposes, producing eunuchs who held positions of power in Byzantine, Ottoman, Chinese, and Roman societies. A cross-cultural historical review found that castrated men were not consistently asexual or celibate. Many remained sexually active, and in certain cultures they were actively sought as sexual partners by both men and women.6PubMed Central. The sexuality and social performance of androgen-deprived (castrated) men throughout history: implications for modern day cancer patients
The degree of retained function varied, and much depended on the age at which castration occurred. Men castrated after puberty, whose bodies had already developed under the influence of testosterone, generally retained more sexual capacity than those castrated before puberty. The historical record is messy and filtered through centuries of cultural interpretation, but the consistent thread is that erection and even sexual activity did not universally vanish after the testes were removed. The authors of that review noted the findings have direct implications for modern cancer patients undergoing androgen deprivation, suggesting that sexual function need not be written off entirely.
Long-Term Changes to Penile Tissue
While erections remain possible in the short and medium term after losing testosterone, the picture gets more complicated over time. Testosterone plays a maintenance role in the structural health of the erectile tissue itself. Without it, the smooth muscle cells in the corpora cavernosa gradually get replaced by collagen and other stiff extracellular matrix proteins, a process called fibrosis. Animal studies have shown that castration leads to reduced smooth-muscle-to-collagen ratios in the penis, along with lower erectile pressure during stimulation.7PubMed. Androgen deficiency impairs erectile function in rats through promotion of corporal fibrosis
Think of it like a sponge slowly stiffening. The erectile chambers need to be elastic to fill with blood and expand. As fibrosis progresses, the tissue becomes less compliant, and erections become weaker even when the neurological signals and blood supply are working properly. This is one reason why testosterone replacement, when medically appropriate, is often recommended sooner rather than later: preserving the tissue architecture matters for long-term function.
In humans, this process unfolds over months and years, not days. A man who loses his testes will not immediately notice a collapse in tissue quality. But the gradual decline in smooth muscle integrity is a real concern for anyone living long-term without androgen replacement.
Why Standard Erectile Dysfunction Drugs May Not Work as Well
Medications like sildenafil and tadalafil work by blocking an enzyme called PDE5, which breaks down the chemical signal that keeps smooth muscle relaxed during an erection. In a normal testosterone environment, this approach works well because there is plenty of nitric oxide and PDE5 in the penile tissue to work with. But in androgen-deprived states, both nitric oxide production and PDE5 levels in the penis decline. Research has found that androgens upregulate PDE5 in penile tissue, and when that hormonal support disappears, PDE5 inhibitors have less to inhibit.8PubMed Central. Testosterone Therapy Improves Erectile Function and Libido in Hypogonadal Men
This creates a frustrating paradox for men in castrate states: the first-line drugs for erectile dysfunction are less effective in the very population that needs them most. It does not mean they are useless. Some men without testes still respond to PDE5 inhibitors, especially if they have residual adrenal androgen production or are receiving some degree of testosterone replacement. But the response rate is lower than in men with normal testosterone levels, and the effect may be weaker.
Alternatives When Pills Fall Short
For men who do not respond adequately to oral medications, other options exist. Intracavernosal injections bypass the nitric oxide pathway entirely by delivering vasodilating drugs directly into the erectile tissue. The most common agent is alprostadil, a synthetic version of prostaglandin E1, which relaxes smooth muscle through a different biochemical route than PDE5 inhibitors. A newer combination of aviptadil and phentolamine has shown promise for men who have not responded to other treatments, with roughly six in ten men in one study finding it effective.9Oxford Academic (The Journal of Sexual Medicine). Intracavernosal injection of aviptadil and phentolamine for refractory erectile dysfunction
For men with spinal cord injuries who can achieve partial erections, simple mechanical solutions like constriction bands can help maintain rigidity. Vacuum erection devices, which draw blood into the penis mechanically, are another option that works regardless of hormonal status. And penile implants, surgical devices placed inside the corpora cavernosa, provide the most reliable erections of any treatment since they are entirely mechanical and do not depend on blood flow, nerve function, or hormones at all.
The point is that the loss of testes narrows the options but does not eliminate them. The treatment ladder has multiple rungs, and men without testes can often find a workable solution by moving to a different one.
Testosterone Replacement and Erectile Recovery
For men who have lost their testes to cancer surgery, trauma, or other medical reasons, testosterone replacement therapy is frequently part of the treatment plan, assuming there is no medical contraindication like active hormone-sensitive cancer. Replacing the missing testosterone addresses the root hormonal deficit directly. Studies have shown that androgen replacement in hypogonadal men significantly improves nocturnal erections, both in frequency and rigidity, confirming that those sleep-related erections are tightly regulated by hormone levels.3PubMed. The effects of testosterone replacement on nocturnal penile tumescence and rigidity and erectile response to visual erotic stimuli in hypogonadal men
Replacement also tends to restore libido, which is often the more noticeable loss. Many men who lose their testes report that the drop in desire is more disruptive to their sex lives than any mechanical difficulty with erections. Testosterone therapy addresses both, and when combined with PDE5 inhibitors, the combination tends to work better than either approach alone. The testosterone restores the penile tissue’s responsiveness to nitric oxide, and the PDE5 inhibitor amplifies whatever signal is present.8PubMed Central. Testosterone Therapy Improves Erectile Function and Libido in Hypogonadal Men
Timing matters. If replacement begins relatively soon after orchiectomy, before significant fibrosis has set in, the tissue is more likely to recover full function. Men who go years without testosterone and then start replacement may find that the structural damage to the erectile tissue limits how much improvement they see, even when hormone levels are normalized.
The Transgender Health Perspective
The question of erections without testes also arises in the context of transgender health. Trans women who undergo orchiectomy as part of gender-affirming care are removing their testes deliberately, and many are already on estrogen therapy that suppresses testosterone. For some trans women, the loss of spontaneous erections is a welcome change that aligns with their gender identity. For others, particularly those who wish to remain sexually active using their existing anatomy, the ability to achieve erections with direct stimulation matters.
The picture looks different for trans men. Some trans men who undergo metaidoioplasty, a procedure that uses testosterone-enlarged clitoral tissue to create a small phallus, retain full erectile function in that tissue. A position statement from the European Society for Sexual Medicine noted that metaidoioplasty preserves sexual arousal, erogenous sensation, and spontaneous erections, with patients reporting no difficulties with arousal, masturbation, or orgasm.10PubMed Central. ESSM Position Statement “Sexual Wellbeing After Gender Affirming Surgery”
These cases illustrate that erectile tissue, wherever it exists in the body, has intrinsic vascular and neurological capacity that does not depend entirely on testicular testosterone. The source of androgens matters (trans men typically take exogenous testosterone), but the tissue itself can function robustly under the right conditions.
Why Age at Castration Matters
One of the most important variables in predicting erectile function after losing the testes is the age at which it happens. A man castrated at 40 has spent decades with testosterone shaping his body, including the development of his penile vasculature, nerve connections, and smooth muscle architecture. Those structures do not vanish overnight. The wiring is established, the tissue is mature, and the system can coast on its existing infrastructure for some time even without ongoing hormonal support.
A boy castrated before puberty is in a fundamentally different situation. Without testosterone during the critical developmental window, the erectile tissue never fully matures. The penis typically remains smaller, the corpora cavernosa are less developed, and the neural pathways that support psychogenic erections may not establish themselves normally. Historical records of prepubertal eunuchs suggest lower sexual capacity compared to those castrated as adults, though as noted earlier, cultural context and individual variation always played a role.
For modern patients, prepubertal castration is rare and almost always the result of medical conditions like bilateral testicular torsion or congenital absence (anorchia) rather than deliberate surgery. Boys in these situations are typically started on testosterone replacement at the age when puberty would normally begin, specifically to support normal development of the reproductive and skeletal systems.
Erections in Non-Mammalian Species
The relationship between testes and erections is not universal across the animal kingdom. Birds, for instance, use an entirely different erection mechanism from mammals. Rather than filling erectile tissue with blood under arterial pressure, most birds that have a penis (many species have lost it entirely) use lymphatic fluid to inflate it. Researchers confirmed that even ratites like ostriches and emus use this lymphatic system rather than a blood-based one, establishing that the evolutionary transition to lymphatic erection happened in the common ancestor of all birds.11CrossRef API. The erection mechanism of the ratite penis
This is more than a curiosity. It underscores that erection as a physical phenomenon is fundamentally about hydraulics, whether the fluid is blood or lymph. Hormones modulate the system, influence desire, and maintain tissue health, but the mechanical event itself is about fluid pressure in expandable tissue. That basic principle is why erections remain possible even in profoundly testosterone-depleted humans: the plumbing still works, even when the chemical signals telling it to activate are quieter than normal.