What Is Cotton Fever? Causes and Symptoms

Cotton fever is a rapid-onset febrile syndrome that affects people who inject drugs intravenously, named for the cotton filters used to strain dissolved drug solutions before injection. What is cotton fever in clinical terms? It is a short-lived but alarming response involving high fever, shaking chills, and muscle pain that appears within minutes of an injection and resolves on its own within hours. In Canada, injection drug use is linked to 18.2% of all new HIV diagnoses recorded in 2023, a figure that reflects just how many broader health risks surround intravenous drug use beyond the drug itself¹.

Key Takeaways

• Cotton fever is a sudden febrile syndrome that follows intravenous drug injection through cotton filters, producing high fever, rigors, and muscle pain that usually resolve within hours.
• The leading medical explanation attributes the condition to endotoxins released by Pantoea agglomerans, a gram-negative bacterium that colonises cotton plants and survives in cotton filter material.
• Reusing old cotton filters, a practice known as shooting the cottons, increases the bacterial load substantially and raises the likelihood of a more severe reaction.
• Cotton fever causes symptoms that closely resemble early sepsis and infective endocarditis, making accurate identification genuinely difficult without clinical evaluation.
• Most episodes resolve without specific medical treatment, but persistent or worsening fever beyond 12 hours warrants immediate emergency evaluation.
• Recurring episodes are a clear clinical signal that injection drug dependence has reached a point where professional residential treatment is needed.

What Is Cotton Fever, and Who Is Most at Risk?

What is cotton fever, and why does it appear almost exclusively in people who inject drugs? The name points directly to the cause. When heroin or other injectable drugs are prepared for use, the powder or residue is dissolved in water and heated, then drawn through a small piece of cotton, a cigarette filter, or a cotton ball before being pulled into the syringe. The filter is meant to trap undissolved particles. It cannot remove the microscopic bacteria that have colonised the fibres themselves.

The syndrome was first documented in clinical literature in 1975, though a similar febrile condition had been noted among cotton farm workers as early as the 1940s. Within fifteen to thirty minutes of injection, the person experiences a sharp rise in body temperature, uncontrollable shaking, and muscle pain. White blood cell counts rise, and the clinical picture closely mirrors the early phase of a serious bacterial infection.

Anyone who injects drugs using cotton as a filter faces some level of risk, but people who save and re-use old cotton filters carry substantially greater exposure. The residual drug that accumulates in used filters draws users back to them, particularly late in a using cycle. Why heroin is so addictive comes down to the drug's intensity and speed of action in the brain; that pull toward injection as the preferred route is what makes cotton filters near-universal in long-term heroin use, and cotton fever an almost certain consequence over time².

What Are the Cotton Fever Causes?

Three competing theories attempt to explain the cotton fever causes. None has been conclusively proven, but one commands substantially more clinical support than the others.

The endotoxin theory holds that gram-negative bacteria, specifically Pantoea agglomerans (previously classified as Enterobacter agglomerans), naturally colonise cotton plants. When cotton filter material enters contact with a heated drug solution, these bacteria release lipopolysaccharide endotoxins into the liquid. Injecting that liquid carries the endotoxins directly into the bloodstream, where they trigger the same inflammatory cascade responsible for fever in many bacterial infections. Blood cultures in cotton fever cases return negative because the fever stems from the toxin and not from live bacterial infection.

The immunologic theory proposes that some individuals already carry antibodies against cotton proteins, producing a hypersensitivity-style reaction and not a toxin-driven one. The pharmacologic theory suggests that pyrogenic compounds within the cotton plant itself, not bacteria, trigger the febrile response.

The most dangerous cotton fever cause in practice is the behaviour known as shooting the cottons, where old filters are boiled or soaked to extract residual drug and the resulting liquid is injected. Used cotton holds a far higher concentration of bacteria than fresh material, amplifying both the endotoxin load and the severity of the reaction².

What Are the Symptoms of Cotton Fever?

The symptoms of cotton fever arrive fast. Most people notice the onset within fifteen to thirty minutes of injection, and the presentation can be severe enough to prompt a visit to an emergency department.

Most episodes resolve within twelve hours, though some persist for up to forty-eight hours. The person will frequently look acutely unwell during an episode, sometimes disoriented or difficult to engage. Leukocytosis (elevated white blood cell count) is common on laboratory testing, occasionally reaching 22,000 per microlitre in documented cases.

The absence of an identifiable bacterial source in blood cultures is one of the key features distinguishing cotton fever from genuine sepsis, though this distinction can only be confirmed after cultures have been incubated for a minimum of twenty-four hours. Until that point, clinicians cannot reliably separate cotton fever from something far more dangerous on clinical grounds alone.

How Is Cotton Fever Distinguished from Serious Infections?

Cotton fever shares so many surface features with life-threatening infections that emergency clinicians frequently admit patients for full sepsis work-ups before cotton fever is confirmed. This overlap is not a clinical failure. It reflects how genuinely difficult the differentiation is in the acute setting.

The most clinically dangerous condition to exclude is infective endocarditis, a bacterial infection of the heart valves that is disproportionately common among people who inject drugs. Unlike cotton fever, endocarditis does not resolve within hours. Fever persists for days to weeks, new heart murmurs may emerge, and embolic signs (small red-brown marks under the fingernails, painful nodules on the fingers) may appear. Sepsis from bacteraemia follows a similar pattern of escalating severity, with signs of organ dysfunction and not spontaneous recovery³.

A person who has had cotton fever before and recognises the pattern may be correct in their self-assessment, but medical evaluation remains the only reliable way to rule out a concurrent infection. Cotton fever has been documented alongside genuine Pantoea bacteraemia in rare cases, meaning the two can co-occur. The clinical guidance is clear. If fever does not begin improving within twelve hours, or if new symptoms appear such as chest pain, shortness of breath, or confusion, emergency care is not optional.

People managing heroin addiction face this diagnostic uncertainty repeatedly, and each unresolved episode carries real risk of missing the transition from a self-limiting syndrome to something requiring hospitalisation.

What Does Cotton Fever Reveal About the Need for Treatment?

Cotton fever is rarely described in medical literature as a primary concern. It registers in the clinical record as a warning sign and diagnostic complication, the reason someone who set out to manage withdrawal ends up in an emergency department. What it reveals, beyond any individual episode, is the depth of physical dependence that drives continued injection drug use regardless of its consequences.

A person experiencing repeated episodes of cotton fever is not making a rational risk calculation and accepting a manageable downside. They are caught in a biological dependency that removes choice from the equation. The same neurological grip of opioid addiction that makes stopping feel impossible also narrows the available responses to discomfort, withdrawal, and financial pressure down to a single familiar one. Use again.

Recovery from injection drug dependence is possible, and the clinical evidence on what works is consistent. Medically supervised withdrawal followed by residential care produces substantially better long-term outcomes than unassisted cessation. At the Canadian Centre for Addictions, clients receive medically monitored detox alongside personalised residential care at two historic Ontario properties, with programme lengths from 30 to 90 days and clinical support from on-site physicians, registered psychotherapists, and certified addictions counsellors.

Ready to Take the First Step?

Addiction doesn't get better on its own. Call us today at 1-855-499-9446 for a free, confidential consultation and find out which programme is right for your needs.

Cotton fever clears in a matter of hours. The addiction driving it does not. Each episode lands a person closer to the more serious infections that cotton fever mimics, and the only way out of that trajectory is treatment that addresses the dependence at its root.

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