Prostaglandins are a family of fat-derived signaling molecules that nearly every tissue in your body produces, and they influence an extraordinary range of processes: pain, fever, blood clotting, kidney filtration, stomach protection, labor contractions, and even the growth of your eyelashes. They are not hormones in the traditional sense because they act locally, right where they are made, and break down within seconds to minutes. That local, short-lived action is what makes them so versatile and, when things go wrong, so difficult to target with drugs without causing side effects elsewhere.
How Your Body Makes Prostaglandins
Prostaglandins start as arachidonic acid, a fatty acid sitting in the membranes of your cells. When a cell is disturbed, whether by injury, infection, or a chemical signal, enzymes called phospholipases clip arachidonic acid free from the membrane. From there, an enzyme called cyclooxygenase (COX) converts it into an unstable intermediate, which is then handed off to different downstream enzymes that each produce a specific type of prostaglandin.1PubMed Central. Prostaglandins and Inflammation Those downstream enzymes are what determine which prostaglandin a given cell produces, and different tissues express different ones.2Proceedings of the Japan Academy, Series B. Prostaglandin terminal synthases as novel therapeutic targets This is why one tissue might churn out a prostaglandin that causes blood vessels to widen while another produces one that makes them clamp down.
There are two main forms of COX. COX-1 is active all the time in most tissues and handles routine housekeeping: protecting the stomach lining, supporting kidney blood flow, helping platelets do their job. COX-2 is mostly quiet until something triggers it, like tissue damage or an immune signal, and then its output ramps up dramatically. That distinction between the “always on” COX-1 and the “inflammation-activated” COX-2 became the basis for an entire generation of anti-inflammatory drugs, with consequences both intended and not.
Pain and Inflammation
When tissue is injured or infected, COX-2 activity surges and the local concentration of prostaglandin E2 (PGE2) climbs sharply. PGE2 does not cause pain by itself in the way a knife cut does. Instead, it sensitizes your nerve endings so that stimuli which would normally be mild, a light touch or a small temperature change, become painful. Researchers have shown that PGE2 can prolong this heightened sensitivity in the nerve cells responsible for detecting damage, which may help explain why inflammatory pain sometimes outlasts the original injury.3PubMed. Peripheral prostaglandin E2 prolongs the sensitization of nociceptive dorsal root ganglion neurons possibly by facilitating the synthesis and anterograde axonal trafficking of EP4 receptors In mouse models, even closely related prostaglandin variants like PGE2-glycerol can sensitize pain-detecting nerve fibers and lower their threshold for heat, cold, and mechanical pressure.4PubMed Central. Sensitization of nociceptors by prostaglandin E2–glycerol contributes to hyperalgesia in mice with sickle cell disease
PGE2 also drives the redness and swelling of inflammation by dilating small blood vessels and making them leaky, allowing immune cells and fluid to flood the area. This is useful when the body needs to fight off bacteria, but it is exactly what makes a sprained ankle throb and swell.
How Prostaglandins Cause Fever
When your immune system detects a systemic infection, immune signaling molecules prompt the brain to ramp up PGE2 production in a region of the hypothalamus called the preoptic area. Normally, neurons in the preoptic area send a steady calming signal to heat-generating centers in the brainstem, keeping your body temperature stable. PGE2 binds to receptors on those preoptic neurons and silences them. Without that calming brake, the heat-generating neurons activate, and your temperature rises.5PubMed Central. Neural Mechanisms of Inflammation-Induced Fever Experiments in guinea pigs demonstrated that PGE2 linked to fever is actually synthesized inside the brain rather than drifting in from the bloodstream; injecting PGE2 outside the brain did not raise brain PGE2 levels or body temperature.6PubMed. Hypothalamic prostaglandin E2 during lipopolysaccharide-induced fever in guinea pigs
This is why aspirin and ibuprofen reduce fever. They block COX activity, cutting PGE2 production in the hypothalamus and letting those preoptic neurons resume their normal job of keeping temperature in check.
The Cardiovascular Balancing Act
In your blood vessels and platelets, two prostaglandin relatives with opposite effects maintain a careful equilibrium. Thromboxane A2, produced by platelets, narrows blood vessels and encourages clot formation. Prostacyclin (PGI2), produced by the cells lining blood vessel walls, does the reverse: it widens vessels and discourages platelets from sticking together.7PubMed. Thromboxane A2, prostacyclin and aspirin: effects on vascular tone and platelet aggregation Healthy cardiovascular function depends on both signals staying in balance. When the balance tips toward too much thromboxane or too little prostacyclin, the risk of clots, heart attacks, and strokes increases.8PubMed. Prostacyclin receptor/thromboxane receptor interactions and cellular responses in human atherothrombotic disease
One place this balance matters acutely is in newborns. Before birth, a blood vessel called the ductus arteriosus connects two major arteries and lets blood bypass the lungs, which are not yet in use. PGE2 is the signal that keeps this vessel open during fetal life.9PubMed. Prostaglandins and the ductus arteriosus Once a baby is born and begins breathing, falling PGE2 levels allow the ductus to close naturally. In premature infants, where PGE2 activity is still high, the ductus sometimes stays open and needs medical intervention.10The Journal of Clinical Investigation. The paradoxical patent ductus arteriosus Conversely, in babies born with certain heart defects where blood flow to the lungs depends on that connection remaining open, doctors administer synthetic PGE1 to keep the ductus patent until surgery can be performed.11PubMed. Prostaglandins, ductus arteriosus, pulmonary circulation: current concepts and clinical potential
Protecting the Kidneys
Your kidneys rely on prostaglandins as a safety net. Under normal conditions, when you are well hydrated and your blood pressure is stable, prostaglandins play a modest role in kidney blood flow. But the moment your body is stressed by dehydration, blood loss, or heart failure, stress hormones constrict blood vessels throughout the body, including those feeding the kidneys. Prostaglandins, especially PGI2 and PGE2 produced by COX-2 in the kidney cortex, push back against that constriction and keep the kidney’s filtering units supplied with blood.12PubMed. Physiological regulation of prostaglandins in the kidney
Block prostaglandin production in this context, say by taking an NSAID while dehydrated, and you remove that protective buffer. The kidneys lose blood flow, and filtering drops.13PubMed Central. Renal Effects of Prostaglandins and Cyclooxygenase-2 Inhibitors This is one of the main reasons doctors warn against using ibuprofen or similar drugs when you are dehydrated, have kidney disease, or are taking blood-pressure medications that already stress kidney perfusion.
Why NSAIDs Hurt Your Stomach
The stomach is an acid bath, yet it does not digest itself because its lining produces a layer of protective mucus and bicarbonate, maintains good blood flow to repair damage quickly, and replaces surface cells on a rapid schedule. Prostaglandins, produced locally by COX-1, coordinate virtually every aspect of this defense.14PubMed. Prostaglandins, NSAIDs, and gastric mucosal protection: why doesn’t the stomach digest itself? When you swallow an NSAID, it inhibits COX throughout the body, including in the stomach lining. With prostaglandin production suppressed, mucus thins, blood flow drops, and the lining becomes vulnerable to the acid it normally resists. That is why long-term NSAID use is a leading cause of stomach ulcers, and why many people take acid-reducing drugs alongside their anti-inflammatory medication.
Prostaglandins in Reproduction and Labor
Prostaglandins play a central role in the reproductive cycle. In many mammals, prostaglandin F2α is the signal that triggers the breakdown of the corpus luteum, the temporary hormone-producing structure in the ovary. That breakdown drops progesterone levels and either allows a new menstrual cycle to begin or, in livestock, signals the end of the reproductive cycle.15Encyclopedia of Reproduction. Luteolysis Prostaglandins also soften and dilate the cervix and stimulate uterine contractions, which is why synthetic prostaglandin drugs are widely used in obstetrics to induce labor.
Two such drugs, dinoprostone (a synthetic PGE2) and misoprostol (a PGE1 analogue), are staples for cervical ripening and labor induction. PGE2 works partly by triggering immune cells that remodel the cervical tissue, while misoprostol more directly stimulates uterine muscle contractions in a dose-dependent manner.16PubMed. The role of prostaglandins E1 and E2, dinoprostone, and misoprostol in cervical ripening and the induction of labor: a mechanistic approach In a randomized trial comparing the two in first-time mothers at full term, misoprostol shortened the time from induction to delivery by several hours and reduced the need for additional oxytocin, though it was associated with a somewhat higher rate of abnormal fetal heart tracings.17PubMed Central. Comparison of Misoprostol and Dinoprostone for elective induction of labour in nulliparous women at full term: A randomized prospective study
How Aspirin and NSAIDs Exploit the Pathway
All traditional NSAIDs, from aspirin to ibuprofen to naproxen, work by blocking COX enzymes and reducing prostaglandin production.18PubMed. Mechanism of action of aspirin-like drugs Aspirin is unique among them because it permanently disables the COX enzyme rather than just sitting in its active site temporarily, which is why a single low-dose aspirin can suppress platelet thromboxane production for the full lifespan of the platelet (about ten days). It also reduces PGE2 in tissues like skeletal muscle.19PubMed Central. Aspirin as a COX inhibitor and anti-inflammatory drug in human skeletal muscle The discovery that aspirin works by blocking prostaglandin synthesis, made by the pharmacologist John Vane roughly 70 years after Bayer first marketed the drug, earned him a Nobel Prize.20PubMed. The first 3500 years of aspirin history from its roots – A concise summary
Because COX-1 handles protective functions (stomach, kidneys, platelets) while COX-2 drives inflammation, pharmaceutical companies developed drugs that selectively block COX-2, hoping to get anti-inflammatory relief without the stomach ulcers. This worked for the stomach, but tipping the prostacyclin-thromboxane balance had cardiovascular consequences. Large-scale analyses found that COX-2 selective drugs and certain traditional NSAIDs like diclofenac increased the risk of major heart events by roughly 40%, driven mainly by a 75% rise in coronary events. Naproxen, which has a more balanced effect on both COX enzymes, did not significantly raise heart risk.21PubMed Central. Cardiovascular effects of cyclooxygenase‐2 inhibitors: a mechanistic and clinical perspective One COX-2 inhibitor, rofecoxib, was withdrawn from the market entirely because of this risk. The episode remains one of the clearest illustrations of how prostaglandin biology punishes you for targeting one part of the system without accounting for the rest.
Prostaglandins in Glaucoma Treatment
One of the more unexpected medical applications of prostaglandin biology is in eye care. Prostaglandin analogue eye drops, such as latanoprost and bimatoprost, are now a first-line treatment for glaucoma. They lower pressure inside the eye by increasing drainage of aqueous fluid through a route called the uveoscleral pathway, without affecting the production of that fluid.22PubMed. Prostaglandin analogues in the treatment of glaucoma The mechanism involves remodeling the tissue between muscle bundles in the ciliary body and sclera: prostaglandin signaling activates enzymes that dissolve collagen in those spaces, opening up channels for fluid to drain more freely.23PubMed Central. Update on the Mechanism of Action of Topical Prostaglandins for Intraocular Pressure Reduction
A notable side effect of these drops is that they stimulate eyelash growth: lashes become longer, thicker, and darker. This happens because bimatoprost increases the proportion of eyelash follicles in their active growth phase and boosts melanin production.24PubMed. Enhancing the growth of natural eyelashes: the mechanism of bimatoprost-induced eyelash growth Pharmaceutical companies noticed and repackaged the same compound as a cosmetic product for eyelash enhancement, which may be the only time in drug history that a side effect from glaucoma treatment became a beauty product marketed on television.
Treating Pulmonary Hypertension
In pulmonary arterial hypertension, the blood vessels in the lungs narrow and stiffen, forcing the right side of the heart to work dangerously hard. Prostacyclin’s ability to widen blood vessels and prevent clotting makes it one of the most effective treatments for this condition.25PubMed Central. Prostacyclin Therapy for Pulmonary Arterial Hypertension Epoprostenol, a synthetic form of prostacyclin delivered through a continuous intravenous pump, rapidly lowers resistance in the pulmonary blood vessels and improves circulation.26PubMed Central. Use of Epoprostenol in the Treatment of Pulmonary Arterial Hypertension The drug is life-saving but demanding: it requires an indwelling central venous catheter and a portable pump that the patient carries at all times, because prostacyclin breaks down so quickly that even a brief interruption in the infusion can cause a dangerous rebound in pulmonary pressure. Newer prostacyclin analogues delivered by inhalation or subcutaneous injection have made treatment somewhat more manageable, but the continuous-infusion version remains the gold standard for severe cases.
Prostaglandins That End Inflammation
It sounds paradoxical, but the same prostaglandins that kick off inflammation also help shut it down. Research has shown that early in an inflammatory response, PGE2 flips a switch inside immune cells that changes which lipid signals they produce. Initially, immune cells arriving at the site of injury generate pro-inflammatory molecules. But as PGE2 accumulates, it triggers those cells to start manufacturing a different class of lipid mediators, called specialized pro-resolving mediators, which actively stop the influx of more immune cells and begin the cleanup process.27PubMed. Lipid mediator class switching during acute inflammation: signals in resolution This lipid-mediator class switching is now understood to be a critical step in the transition from active inflammation to resolution.28PubMed Central. Lipid Mediators in the Resolution of Inflammation
This dual role complicates the simple story that prostaglandins are “bad” because they cause inflammation. Blocking them entirely with NSAIDs may relieve symptoms but could also delay or impair the resolution phase. Whether this matters clinically for, say, recovery from a muscle injury or a surgical procedure is still debated, but the biology suggests that the inflammatory process needs its prostaglandin phase to know when and how to stop.
The Link to Cancer
Tumors are not just masses of dividing cells; they build a local environment that shields them from the immune system. PGE2 is emerging as one of the key molecules tumors use to do this. Cancerous tissue often overexpresses COX-2, flooding the area with PGE2, which promotes blood vessel growth into the tumor, stimulates tumor cell survival and migration, and, perhaps most importantly, suppresses the anti-tumor immune response.29PubMed Central. Role of prostaglandin E2 in the progression of gastrointestinal cancer One key mechanism involves PGE2 disabling a type of immune cell called a conventional dendritic cell, which normally orchestrates the killer T cells that attack tumors. In mouse models, blocking the PGE2 receptors EP2 and EP4 on these dendritic cells prevented their dysfunction, reinvigorated the local T cell response, and achieved immune control of tumors.30Immunity. Tumor-derived prostaglandin E2 programs type 1 conventional dendritic cell dysfunction to promote immune evasion
This is one reason epidemiological studies have found that long-term aspirin use is associated with lower rates of colorectal cancer. By inhibiting COX-2 and reducing PGE2 in the gut, aspirin may deprive precancerous growths of one of their immune-evasion tools. The idea of combining PGE2 receptor blockers with immunotherapy drugs is an active area of cancer research, with the hope that removing the prostaglandin shield will let the immune system do what it was designed to do.31Pharmacological Reviews. Prostaglandin E2 in the Tumor Microenvironment, a Convoluted Affair Mediated by EP Receptors 2 and 4
Prostaglandin Receptors and Why They Matter
PGE2 alone acts through four different receptor subtypes, called EP1 through EP4, each of which activates a different signaling pathway inside the cell. EP1 triggers calcium signaling, EP2 and EP4 raise levels of a second messenger that broadly relaxes smooth muscle and modulates immune responses, and EP3 does something closer to the opposite. This means the same prostaglandin molecule can have wildly different effects depending on which receptor the target cell expresses.32PubMed Central. Structural insights into the activation of the human prostaglandin E2 receptor EP1 subtype by prostaglandin E2 The receptor landscape helps explain apparent contradictions, like PGE2 being pro-inflammatory in one tissue and pro-resolving in another, or promoting fever in the brain through EP3 while protecting kidney blood flow through EP2 and EP4.
For drug developers, these receptors represent a chance to be more precise than a sledgehammer COX inhibitor. Instead of blocking all prostaglandin production and dealing with the fallout in the stomach, kidneys, and cardiovascular system, you could target a single receptor subtype in a specific tissue. Progress has been slow because the receptor structures were not well understood until recently, but structural biology is now catching up, with high-resolution maps of each EP subtype becoming available.
Ancient Molecules Found Across the Tree of Life
Prostaglandins are not a vertebrate invention. The COX enzyme that produces them has been found in corals, and researchers believe COX activity likely occurs widely across all multicellular invertebrates, suggesting the coral version is the evolutionary ancestor of vertebrate COX-1 and COX-2.33Journal of Experimental Biology. Prostaglandins in non-insectan invertebrates: recent insights and unsolved problems Even more surprising, an active prostaglandin pathway resembling the animal version has been identified in marine diatoms, single-celled photosynthetic organisms that are about as far from a human as a living thing can be. The discovery opens up the possibility that prostaglandins serve as cell-to-cell signaling molecules in the ocean, potentially influencing how plankton populations grow and crash.34PubMed Central. Animal-like prostaglandins in marine microalgae
The fact that prostaglandin signaling is conserved from single-celled algae to humans speaks to how fundamental the underlying chemistry is. These molecules are not a recent patch bolted onto the immune system; they are woven into the basic operating software of complex life. When you take an ibuprofen for a headache, you are temporarily interfering with a signaling system that has been running, in one form or another, for hundreds of millions of years.