Rashes, Earaches and Skin Infections From Swimming Pools and Hot Tubs

The most common types of illness from swimming pools and hot tubs, known as recreational water illnesses (RWIs), include rashes, earaches, and skin infections. Most illnesses are minor and resolve on their own without medical treatment. These minor illnesses are termed "self-limiting" in medical terminology. Occasionally, some infections can become more serious and may be life-threatening if not treated medically. Understanding how and why these RWIs occur is important for ensuring the health and safety of all patrons and employees.

TYPES OF RASHES AND SKIN INFECTIONS

The two major categories of rashes are allergic reactions and infections. These look similar in many cases, even to doctors. The best way to distinguish types of rashes is to understand how they are initiated. Allergic reactions are the body’s response to foreign chemicals in the water. Infections are caused by a foreign organism, typically a bacterium or virus, invading the body and growing. In both cases, the body’s immune system identifies the foreign material and launches a cascade of self-defense mechanisms.

Irritant contact dermatitis.Photo has been released into the public domain

IRRITANT AND ALLERGIC REACTIONS

Rashes that happen quickly or within a few hours of swimming are most likely irritation caused by the body’s immune system reacting to chemicals in the water. The medical term for this type of rash is irritant contact dermatitis. Irritation reactions happen quickly. In many cases, the redness and itchiness occur within a few minutes after leaving the water but may take up to 24 hours before they are noticed.

In nearly all cases, the cause of the allergic reaction is combined chlorine (chloramines, more properly called disinfection byproducts or DBPs). One study found up to 14.7% of swimmers developed some amount of rash while swimming, but the reports of rashes dropped substantially when the pool was properly oxidized to limit combined chlorine (Kelsall and Sim. 2001). Over 800 chloramines have been identified in chlorine-treated water. Not all of these are irritating. Some people are much more sensitive than others, so not everyone that swims in a pool will have the same reaction.

Irritations and contact dermatitis are well documented in brominetreated pools and hot tubs. The DPD test cannot distinguish between free and combined bromine. Although the specific irritant is often unknown, it is likely that combined bromine species (bromamines) are involved, and irritation is frequently reported with higher concentrations of bromine. Clinical investigations of four distinct cases confirmed that the affected individuals did not exhibit reactivity to the BCDMH type of bromine tablets. However, they did react to the pool water (Rycroft and Penny, 1983; Fitzgerald et al., 1995).

A small number of people do become allergic to chlorine and bromine. Allergies of this type are called allergic contact dermatitis. They develop over time as the person is repeatedly exposed to the same or closely related chemical. This type of pool rash is almost exclusively limited to individuals who spend many hours in the pool each day and do so over many years. Aquatic physical therapists are the individuals most likely to develop this allergic reaction. The repeated exposure results in hypersensitivity, with individuals reacting to even minuscule amounts of chlorine that would not react with a standard pool test kit. The reactions may become so severe that they are unable to enter even well-maintained pools (Lazarov, et al., 2005).

In most cases, there is no crossreactivity between chlorine and bromine contact dermatitis reactions. This supports the idea that the causative agents are the respective halogenated organic compounds. However, repeated exposure to either chloramines or bromamines can lead to more generalized allergies. In extreme cases, typically involving hypersensitivity reactions, individuals may become cross-reactive such that any exposure to either chlorine or bromine will produce a pronounced reaction. This is summarized in Table 1 below.

INFECTIONS

Infections result when bacteria invade the body and multiply. Infections of the ears, skin, and eyes are generally mild, and most do not require medical treatment. Even though they are mild, infections are indicators that the person was exposed to a bacteria or other microbe, and the source should be investigated.

EARACHES

Earaches are the most common type of recreational water illness (RWI). Earaches are called otitis externa in medical terms. Acute otitis externa can be painful, itchy, and cause swelling and drainage of the outer ear. Extended contact with water may reduce the protective layer of ear wax (cerumen) and leave the tissue more susceptible to infection. The U.S. Centers for Disease Control and Prevention (CDC) recently assessed illnesses transmitted through water and estimated the number of cases in three categories: potable, recreational, and non-potable/non-recreational water. They estimated that each year, there are 4,430,000 cases of earaches after swimming, which resulted in 538,000 visits to emergency departments for medical treatment. This amounted to 78% of all illnesses from recreational water at a total annual cost of $536,000,000 (Gerdes, et al., 2023). In these cases, the recreational water included treated water such as swimming pools and untreated water such as lakes, rivers or streams.

The CDC estimates that 81% of ear infections are due to the bacterium Pseudomonas aeruginosa [read on for more on Pseudomonas]. In other cases, the infection is due to normal microbes from the skin and ear (endogenous microbial flora). The water retained in the ear canal permits the bacteria and other microbes to have an extended survival time. Once the protective ear wax has been removed, the microbes are able to penetrate the skin and begin to grow.

RASHES

Skin rashes are common in under-treated swimming pools and even more common in under-treated hot tubs. Rashes caused by infections are often referred to as "hot tub rash." Swimming or soaking in warm aquatic venues elevates the body temperature and results in perspiration and dilation of the pores of the skin. Bacteria and other microbes that are in the water may then enter the pores. If the bacteria can survive inside the pore, they can begin to grow and multiply. Fortunately, there are few microbes that can survive — let alone multiply — inside the pore.

Typical appearance of a Pseudomonas aeruginosa infection.Photo courtesy James Heilman, MD

PSEUDOMONAS AERUGINOSA

Pseudomonas aeruginosa is a hardy bacterium that thrives in manmade water systems including drinking water, fountains, humidifiers, swimming pools, and hot tubs. There are other species of Pseudomonas, but the only one of concern in aquatic settings is Pseudomonas aeruginosa. Pseudomonas is widely distributed in nature. When it inadvertently enters into the human body, it may cause a variety of infections including earaches, skin infections (folliculitis) and rarely more serious systemic deep infections including septicemia (blood poisoning). A recent study by the CDC estimated that 50% of the infections from recreational water were caused by Pseudomonas aeruginosa (Gerdes, et al., 2023). Investigations of outbreaks frequently identify issues such as inadequate training of operators, incomplete or absent chemical logbooks, and inconsistent disinfectant dosing (Lamere, et al., 2024). A thorough review of outbreak investigations did not identify any Pseudomonas infections in pools or hot tubs that were adequately chlorinated.

Pseudomonas aeruginosa grows slowly in refrigeration but thrives up to 107 degrees Fahrenheit, using various organic compounds while enduring prolonged periods of starvation. It invades pre-existing biofilms where it survives for extended periods. In recently cleaned or new systems, such as newly installed hot tubs or new sand in filters, biofilm can develop quickly. The cells inside the biofilm exist in a near catatonic state awaiting the introduction of new nutrients. Inconsistently maintaining the concentration of chlorine encourages the development of biofilms laden with Pseudomonas aeruginosa. The pattern of consistently treating the water limits the competing microbes that would normally help to control the total population of Pseudomonas aeruginosa. Thus, immediately after the pool or hot tub is used and the chlorine concentration is low, due to the bather load, the Pseudomonas aeruginosa exit the biofilm and migrate into the water. Once in the water, they consume the organic matter introduced by the swimmers or soakers and multiply. Unless it is treated promptly, the pool or hot tub becomes loaded with actively growing — and hungry — bacteria over the next 12 to 48 hours. Any users entering the water after this period may become infected.

Infection by Pseudomonas aeruginosa is a stepwise process. First, the water becomes infested with more than 1,000 bacterial cells per milliliter due to inadequate disinfection. Secondly, the person enters the water and stays wet generally for at least 30 minutes. During this time, the freeswimming bacteria contact the skin and invade the pores of the skin (the hair follicles). The longer the person stays wet, the greater the exposure time. Tight-fitting and lined bathing suits retain water. Even after the person leaves the water, this retained water extends the contact time and increases the risk of infection. Thirdly, once the bacteria are inside the follicle, they begin to consume any organic material and multiply. This is the beginning of the infection. The fourth stage is the body’s immune system responding to the infection. This results in the characteristic reddening, swelling, and localized inflammation. In typical cases, the reddening bumps and itching are first noticed at least 24 hours after swimming or soaking. As the immune system activates to contain the infection, the inflammation worsens for several more days. By this point, the bacteria are dead, and the inflammation is the result of cellular and humoral components of the immune system actively digesting the debris of the dead bacterial cells. If the infected person seeks medical treatment at this point, the rash may be misdiagnosed as a chemical irritation rather than the later phase of a bacterial infection. Attempts to recover live bacteria from the infected follicles more than a day or two after the rash develops are seldom successful. The average duration of the rash from exposure to resolution is 14 days, and the majority do not need medical treatment. In rare cases, the infection enters more deeply into the body and results in a much more serious infection. These cases require hospitalization and antibiotic treatment, often using intravenous and supportive care.

The areas of the body that develop a rash include the legs, trunk, arms, pelvis, buttocks, back, and to a lesser extent, the neck, face, ears, and hands. Women and children tend to experience more widespread rashes. This is likely due to the nature of swimwear for women and the extended time children spend in the water compared to adults. In both cases, prolonged exposure to bacteria-laden water increases the likelihood of infection (Hudson et al., 1985; Khabbaz et al., 1983).

Pseudomonas aeruginosa is readily killed by chlorine. However, the bacteria buried deep inside the biofilm are likely to survive super chlorinating shock treatments. Chlorine quickly reacts with the surface layer of the biofilm and penetrates a short way into the biofilm before it is inactivated. Thus, only the outermost bacterial cells are killed, and the deeply buried cells survive. These survivors are then able to digest the dead cells and begin to regrow the biofilm. If the dose of chlorine was not sufficient to completely satisfy demand and establish a residual, the regrowth of the surviving bacteria may break free from the reformed biofilm and enter the water in search of new nutrient sources. The easiest way to understand this is to think of the bacteria inside the biofilm like a deck of 52 playing cards. The chlorine penetrates 10 to 15 cards but leaves the bottom 37 to 42 cards untouched. This cycle of partial treatment, biofilm regrowth, and liberation of free-swimming bacteria is what happens in pools and hot tubs that do not continuously maintain a residual of at least one ppm of free chlorine.

STAPHYLOCOCCUS

In the past, Staphylococci were suspected of being a cause of rashes in recreational water. There are no documented cases of swimmers or soakers developing rashes from any species of Staphylococcus, including MRSA strains. One suspected waterborne outbreak was ultimately traced to shared razors and towels by members of a swim team (Begier, et al., 2004).

With the exception of cryptosporidium, most recreational water illnesses can be prevented by simply maintaining proper free chlorine levels and ensuring the pH does not exceed the APSP-11 American National Standard for Water Quality in Public Pools and Spas maximum standard of 7.8. Preventing illness in pools and spas requires operators and staff be skilled at maintaining effective levels of disinfection, proper circulation and water balance at all times.

This article first appeared in the May 2025 issue of AQUA Magazine — the top resource for retailers, builders and service pros in the pool and spa industry. Subscriptions to the print magazine are free to all industry professionals. Click here to subscribe.