Table of ContentsView AllTable of ContentsHeat Rash vs. Sun PoisoningHeat Rash CausesHeat Rash Symptoms and TreatmentSun Poisoning CausesTreat and Prevent Sun PoisoningSeeking Medical Care
Table of ContentsView All
View All
Table of Contents
Heat Rash vs. Sun Poisoning
Heat Rash Causes
Heat Rash Symptoms and Treatment
Sun Poisoning Causes
Treat and Prevent Sun Poisoning
Seeking Medical Care
Spending time in the sunshine is an excellent way to boost your mood and vitamin D levels, but too much sun exposure harms your skin and can lead toheat-related illnesses, like heat rash and sun poisoning (severe sunburn).
While heat rash and sun poisoning share similarities, they have distinct causes and require different treatments.
This article discusses the differences between heat rash and sun poisoning, what causes these commonskin rashes, and how to tell the difference. It also covers treatment and prevention.
Pollyana Ventura / Getty Images
Heat Rash vs. Sun Poisoning: How to Tell the Difference
While heat rash and sun poisoning are both heat—and sun-related skin problems, they have distinct causes and characteristics. Knowing the difference can help you identify which you have and determine the most appropriate treatment and prevention methods.
What Causes a Heat Rash?
This photo contains content that some people may find graphic or disturbing.See PhotoReproduced with permission from ©DermNetwww.dermnetnz.org2023
This photo contains content that some people may find graphic or disturbing.See Photo
This photo contains content that some people may find graphic or disturbing.
Reproduced with permission from ©DermNetwww.dermnetnz.org2023
Heat rash, or “prickly heat,” looks like a cluster oftiny red or purple bumpsor pimple-like blisters.Normally, sweat flows through sweat ducts onto the skin’s surface, where it evaporates to keep your body cool during hot weather or when your body temperature rises (e.g., during exercise).
Sweatingmore than usual can block your sweat ducts. Heat rash develops when your sweat glands are clogged, trapping sweat under your skin. Anyone can develop heat rash, though it is most common in infants andyoung childrenwith underdeveloped sweat glands.
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Hot and Humid Weather
People living in cooler climates are more likely to develop heat rash when visiting a location with warm, humid weather. Sudden temperature changes (e.g., cool to hot and humid) can also increase the risk of heat rash.
What Causes Heat Rash?
Physical Activity
Physical activities, such as exercise or strenuous labor, cause you to sweat more than usual. When sweat accumulates and becomes trapped under the skin, heat rash can develop in body areas such as the neck, back, chest, and inner elbows. Repetitive movements during physical activity also create friction between skin surfaces or the skin and clothing, contributing to the development of heat rash.
Synthetic or Tight Clothing
Wearing tight clothing or clothes made from synthetic fabrics increases the risk of heat rash, especially in hotter weather. Synthetic fabrics (e.g., polyester, nylon) are generally less breathable than natural fibers like cotton and can restrict airflow, trapping heat and moisture against the skin. This can clog sweat ducts and lead to heat rash.
Wearing tight-fitting clothes increases sweating and createsfriction between your skin and clothing.The combination of friction, increased sweating, and inadequate airflow for sweat to evaporate increases the likelihood of developing a heat rash.
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Overheating
Anything that causes your body to overheat, such as afever, wearing too many layers of clothing, or sleeping under thick blankets, can increase sweat production, block sweat ducts, and trigger heat rash.
Sweating is your body’s natural cooling mechanism, but if sweat cannot evaporate efficiently due to humid conditions or prolonged overheating, moisture and heat accumulate on the skin’s surface, leading to heat rash.
Heat rash symptoms typically develop within minutes to hours after spending time in hot, humid weather or sweating. It is most common to develop heat rash in areas where there is friction with clothing or skin folds, such as the:
When heat rash symptoms develop, they can include:
Heat rash treatmentinvolves limiting exposure to heat and humidity and keeping your skin cool and dry. Most cases of heat rash clear up within three days with self-care measures, such as:
What Causes Sun Poisoning?
Reproduced with permission from © DermNetdermnetnz.org2023.
Sun poisoningis a severe sunburn that happens when the sun’s ultraviolet (UV) rays damage your skin cells, triggering inflammation that leads to symptoms such as:
People with lighter skin are more likely to develop sun poisoning than people with darker skin because they have less melanin.Melaninis a brown pigment your body makes to block harmful UV rays and protect your skin.
Sun poisoning occurs when exposure to the sun’s UV rays exceeds melanin’s ability to protect your skin. Sun poisoning symptoms typically develop within a few hours and peak (are at their worst) between six and 48 hours after sun exposure.
How to Treat and Avoid Sun Poisoning
If you develop sun poisoning, the first thing to do is seek shade or stay indoors until your symptoms subside. In some cases,self-care measuresmay be enough to treat sun poisoning. Here’s how to treat sun poisoning at home:
More severe sun poisoning requires prompt medical treatment. Depending on the severity of your symptoms, you may need treatment in a hospital to control pain and hydrate your body. Medical therapies for sun poisoning include:
Taking proactive measures to protect your skin from the sun’s UV rays is the best way to avoid or prevent sun poisoning. This includes:
When to Contact a Healthcare Provider
While most cases of heat rash and sun poisoning are manageable with at-home treatments and self-care measures, certain symptoms warrant medical attention. If you suspect you or your child have heat rash, see a healthcare provider if the following apply:
Severe sun poisoning requires medical attention and treatment. See a healthcare provider as soon as possible if you experience any of the following:
A Word From VerywellPeople often confuse heart rash and sun poisoning since they occur in hot and humid conditions and look similar. However, sun poisoning can affect the whole body—rather than areas prone to sweat as with heat rash—and can be more severe if left untreated, requiring a visit to a healthcare provider or emergency room.—WILLIAM TRUSWELL, MD, MEDICAL EXPERT BOARD
A Word From Verywell
People often confuse heart rash and sun poisoning since they occur in hot and humid conditions and look similar. However, sun poisoning can affect the whole body—rather than areas prone to sweat as with heat rash—and can be more severe if left untreated, requiring a visit to a healthcare provider or emergency room.—WILLIAM TRUSWELL, MD, MEDICAL EXPERT BOARD
People often confuse heart rash and sun poisoning since they occur in hot and humid conditions and look similar. However, sun poisoning can affect the whole body—rather than areas prone to sweat as with heat rash—and can be more severe if left untreated, requiring a visit to a healthcare provider or emergency room.
—WILLIAM TRUSWELL, MD, MEDICAL EXPERT BOARD
Summary
Heat rash and sun poisoning are two common heat-related skin problems. Heat rash appears as tiny red or purple bumps from trapped sweat, usually in the neck, back, groin, or armpits. It develops within hours of sweating and clears up with simple measures like cool showers and wearing breathable clothing.
Sun poisoning can develop up to 24 hours after spending too much time in the sun. It may cause incredibly painful and red skin, blisters, fever, nausea, and chills. Treatment depends on the severity of symptoms and may include staying out of the sun, cool compresses, or in-hospital intravenous fluids in severe cases.
Talk to a healthcare provider if you are unsure if you have a heat rash, sun poisoning, or another heat-related illness or rash.
16 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Centers for Disease Control and Prevention.Warning signs and symptoms of heat-related illnesses.
U.S. Department of Veterans Affairs.Sunburn (sun poisoning).
American Academy of Family Physicians.Heat rash.
MedlinePlus.Sweating.
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Baker LB.Physiology of sweat gland function: the roles of sweating and sweat composition in human health.Temperature (Austin). 2019;6(3):211-259. doi:10.1080/23328940.2019.1632145
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Halász M, Geršak J, Bakonyi P, et al.Study on the compression effect of clothing on the physiological response of the athlete.Materials (Basel). 2021;15(1):169. doi:10.3390/ma15010169
American Academy of Dermatology Association.How to prevent and treat common summer rashes.
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American Academy of Dermatology Association.How to treat sunburn.
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Centers for Disease Control and Prevention: The National Institute for Occupational Safety and Health.NIOSH fast facts: protecting yourself from sun exposure.
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