Heat rash vs. sun poisoning

Heat rash is a skin condition caused by blocked sweat ducts, while sun poisoning is a severe sunburn. Heat rash and sun poisoning may look similar at first, but they have different causes, symptoms, and treatments.

Read on to learn more about the differences between heat rash and sun poisoning, and find out how to treat them.

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What is heat rash?

What is sun poisoning?

What is heat rash?

Heat rash, also known as miliaria, is a common condition that occurs when pores become blocked and sweat can’t escape. This can lead to irritation, itching, and a rash.

Heat rash is particularly prevalent in hot and humid conditions and can affect individuals of all ages, though it is more common in babies and young children due to their underdeveloped sweat glands.

Recurring heat rash that fails to properly heal can increase the risk of developing skin infections from bacteria entering broken blisters.

What is sun poisoning?

Sun poisoning is a severe sunburn resulting from excessive exposure to ultraviolet (UV) radiation, which provokes an extreme inflammatory reaction in the cells.

When the skin absorbs too many UV rays without adequate protection, the radiation overwhelms the body's defenses against sun damage. This brings on symptoms ranging from dizziness and fever to chills, blisters, and low blood pressure in severe cases.

In addition to the short-term effects, repeated incidents of severe sun poisoning significantly raise your lifetime risk of skin cancer and premature aging.

Key differences between heat rash and sun poisoning

These are the main differences between heat rash and sun poisoning:

Types

Different types of heat rash and sun poisoning are characterized by symptoms and severity.

Types of heat rash

The three main types of heat rash are:

Miliaria Crystallina: the mildest form, characterized by clear, fluid-filled bumps that easily burst. This type does not typically cause pain or itching and is more common in infants.
Miliaria Rubra: also known as prickly heat, this occurs deeper in the skin and is marked by inflamed, blister-like bumps and a sensation of itching or prickling. It is more common in adults than in children.
Miliaria Profunda: a less common form that affects the deepest layer of the skin, causing firm, inflamed bumps that may be painful or itchy.

Types of sun poisoning

There are two main types of sun poisoning, which vary based on the severity of symptoms:

Mild sun poisoning: characterized by red, warm skin that is painful to the touch. Other symptoms may include small blisters, headaches, and fatigue. This milder form of sun poisoning often clears up in a few days.
Severe sun poisoning: leads to more intense burns, blisters, chills, fever, nausea, dehydration, and extreme pain and tenderness. Symptoms may worsen 12-24 hours after sun exposure. This more extreme reaction often requires medical treatment.

Causes

While both heat rash and sun poisoning stem from unprotected exposure to the sun, the causes differ.

Heat rash causes

Here are some typical causes of heat rash:

Sweat: when sweat ducts become blocked, sweat can't reach the skin's surface to evaporate which leads to inflammation and rashes. Excessive sweating in hot, humid environments often triggers heat rash.
Tight clothing: clothes that rub, cling too tightly, or don't allow ventilation can cause irritation, plug sweat ducts, and worsen heat rash.
Age: infants and children are more prone to heat rash since their sweat ducts are not fully developed. As we age, skin also loses elasticity making it more vulnerable.
Activities: exercise, sports, hard labor, or other physical activities in hot environments cause excessive sweating that contributes to blocked pores and rashes.
Environment: hot, humid weather prevents sweat from evaporating off the skin which can clog pores.
Health conditions: diseases that cause fever or compromise the sweat glands can make heat rash more likely since the body can't cool itself effectively.
Skin infections: bacterial or fungal infections on the skin can spread to sweat ducts, inflaming pores and triggering a rash.

Sun poisoning causes

Here are some of the common causes of sun poisoning:

Sun rays: UVA rays penetrate deeply into the skin, contributing to long-term skin damage and aging. UVB rays burn the skin's surface and can damage the DNA in skin cells. Excessive UV radiation can overpower the skin's melanin, which normally protects against sun damage.
Reflection: surfaces like water, sand, and snow can reflect ultraviolet rays, increasing the intensity of exposure.
Duration: spending long periods of time in the sun without adequate protection increases the risk of sun poisoning.
UV index: being outside during peak UV index hours leads to sun poisoning much faster than off-peak hours.
Location: those in proximity to the equator experience stronger UV radiation.
Environment: UV exposure is more intense at higher altitudes.
Treatments: some medications can increase the skin's sensitivity to UV rays, increasing the risk of sun poisoning.
Immune suppression: damaged skin cells can suppress the immune system, and the body's immune response to skin repair can be compromised, leading to sun poisoning.

Symptoms

Sun poisoning and heat rash may also differ in symptoms.

Symptoms of heat rash

Here are some typical symptoms to watch for with heat rash:

Red clusters of small blisters or bumps on the skin that cause itching or prickling sensations are a hallmark of heat rash.
The rash often occurs on parts of the body prone to sweating and friction, like the neck, chest, groin, or folds of skin.
In infants, heat rash may emerge as dots or tiny pimples surrounded by red skin.
Symptoms usually disappear shortly after cooling the skin, though the rash may briefly reappear with additional heat exposure.
Miliaria rubra leads to small, red, inflamed blisters that can cause a painful, prickly sensation.
Miliaria profunda manifests as deep skin bumps that may be tender, swollen, and painful to the touch.
Symptoms typically clear within days as blisters dry out and peel away, though the skin may remain irritated for longer.

Symptoms of sun poisoning

Here are some of the common symptoms of sun poisoning to look out for:

Skin redness is one of the earliest signs of sun poisoning.
Sun poisoning often leads to intense blistering. Sunburned skin may start peeling away in large, unbroken sheets, indicating a deeper level of skin damage.
Individuals may experience a fever and chills, symptoms not typically associated with a mild sunburn. Dizziness and other heat-related symptoms may also manifest.
Nausea, vomiting, upset stomach, and other flu-like symptoms can manifest.
A rapid heartbeat or heart rate fluctuations, often with low blood pressure and shortness of breath, can accompany sun poisoning.
A sun poisoning rash can break out over large patches of skin.
Some people may experience severe pain, while others may not.

Treatments

Here are some treatment options for these skin conditions.

How to treat heat rash

Here are some common treatments for heat rash:

Cool the skin by moving to a cooler environment, taking a cool bath, or placing damp cool cloths on the rash. This helps soothe the rash and unblock sweat ducts.
Keep the rash dry since moisture worsens the rash. Let the skin air dry after bathing and use light, breathable fabrics.
Use an over-the-counter hydrocortisone cream to reduce swelling and itching. Mild steroid creams help calm inflammation.
Apply a gentle, fragrance-free moisturizer to ease tight, itchy skin but avoid oil-based products.
Use an antimicrobial powder containing zinc oxide or cornstarch to help dry out the rash.
Reduce friction over the rash by wearing loose clothing and protecting against chafing.
Drink plenty of water and avoid consuming excess salt or caffeine to prevent dehydration.
Take an oral antihistamine containing diphenhydramine to relieve severe itching.
See a doctor for diagnosis and prescription medication if rashes are widespread, painful, or don't improve with home treatment.

How to treat sun poisoning

This is how you should treat sun poisoning:

Get out of the sun immediately and move to a shaded, cooler environment.
Take a lukewarm bath or use cool, damp cloths to help soothe and hydrate burned skin. Avoid rubbing or abrasion.
Apply aloe vera gel liberally over sunburned areas to provide a gentle, cooling sensation and aid healing.
Take an over-the-counter pain medication like ibuprofen or acetaminophen to relieve swelling, pain, and headache.
Drink plenty of fluids over the next few days to prevent dehydration and replenish electrolytes.
Use a moisturizer containing antioxidants and natural oils like lavender oil to nourish damaged skin.
Do not break any blisters that form—keep the area clean to prevent infection.
Use hydrocortisone if intense itching occurs after a few days. Antihistamines can also reduce itching.
See a doctor right away if you experience nausea, chills, fever, or confusion which may indicate heat stroke.

Prevention

Prevent sun poisoning and heat rash with these safe sun practices.

How to prevent heat rash

Here are some tips to help prevent heat rash:

Wear loose, breathable fabrics like cotton or moisture-wicking athletic wear that allow sweat to evaporate. Avoid non-breathable synthetics.
Change out of sweaty clothes and shower after heat exposure using lukewarm rather than hot water.
Use fans, air conditioning, and other cooling measures in hot environments. Take regular breaks in the shade if working outdoors.
Keep the skin clean and dry since trapped sweat exacerbates rashes. Change baby diapers frequently.
Apply antiperspirant gently to problematic body areas prone to excessive sweating like the groin, armpits, or skin folds.
Drink enough fluids to prevent dehydration and overheating. Choose water over-caffeinated and alcoholic beverages.
Allow the skin to air dry fully after bathing before dressing to prevent trapping moisture and clogging pores.
Use protective padding or powder to shield areas vulnerable to chafing and friction rashes.

How to prevent sun poisoning

Follow these practices to prevent sun poisoning:

Apply broad-spectrum sunscreen with an SPF of 30 or above to all exposed skin at least 20 minutes before sun exposure. Reapply frequently.
Seek shade during peak sun hours between 10 am and 4 pm, when UV rays are most intense.
Wear wide-brimmed hats, UV-blocking sunglasses, and tightly-woven, loose-fitting UPF clothing that covers more skin.
Gradually increase the amount of time spent in the sun to help the skin build a slight tolerance and reduce the risk of sun poisoning.
Stay hydrated by drinking plenty of cool fluids to avoid dehydration and help regulate body temperature.
Wear full-coverage clothing, like our men’s long-sleeved rash guards or one of our women’s swim dresses to keep your upper body protected.
Use a UV index tracker to monitor daily intensity levels and plan outdoor time accordingly.

How long does a heat rash last?

A heat rash typically lasts between a few hours to a few days.

Mild forms like miliaria crystallina may clear up within hours once the skin has cooled down. The bumps fade without bursting.
Miliaria rubra (prickly heat) rash and symptoms may persist for 3-4 days before the small, red bumps begin to disappear. Full recovery usually occurs within a week.
The deeper bumps of miliaria profunda tend to last the longest (around a week) before subsiding. Healing the irritated thick skin and rash can take 1-2 weeks.
If a heat rash persists longer than a few days or spreads, it's best to see a doctor to rule out other skin conditions. Recurring heat rash also warrants medical attention.
Factors such as continuous sweating, using irritating products, or having an underlying condition can make a heat rash stick around longer before it heals.

So while a mild heat rash may vanish in a matter of hours, moderate to severe rashes can take up to 1-2 weeks to completely clear up.

How long does sun poisoning last?

Sun poisoning can last anywhere from a few days to a couple of weeks depending on the severity.

Milder sun poisoning with some redness, pain, and peeling may start improving within 2-5 days as the damaged skin begins healing.
Moderate cases with blisters, fever, and nausea may persist 5-10 days before symptoms fully clear, as the body repairs more extensive skin injury.
Severe reactions with widespread burning, blistering skin, and extreme pain can last 10-14 days. Extensive skin peeling occurs and new skin needs to regenerate.
It can take up to 6 weeks until sun poisoning burns are completely healed, though most symptoms will resolve sooner. Areas may remain tender and sensitive to sun for 1-2 months.
Lingering symptoms for longer than two weeks may indicate an infection or other complication requiring medical treatment.

Less severe sun poisoning heals in under a week, while more extensive damage could take 2 weeks to 6 weeks to fully heal after UV overexposure.

Heat rash vs. sun rash

Heat rash and sun rash are two distinct conditions that typically occur during warmer months or in sunny environments. Understand the differences between them for proper treatment and prevention.

Heat Rash

Caused by clogged sweat glands and inflamed sweat ducts due to heat and humidity
Appears as small red bumps or blisters, often in areas prone to sweating
Sensations of itching, prickling, or stinging in the rash
Typically occurs on the neck, chest, groin, elbow creases
Goes away once the skin is cooled and dried out

Sun Rash

Caused by a reaction to UV exposure
Rash made up of small red bumps or blisters from contact dermatitis
Often occurs shortly after sunscreen application
Can appear anywhere sunscreen is applied but more common on the face, back, and shoulders
Rash is itchy, irritated, or burning
May resemble symptoms of sun poisoning if UV exposure occurs

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Heat rash vs. sun poisoning FAQ

Can too much sun cause heat rash?

Too much sun exposure does not cause heat rash directly, but it does play a part. Heat rash results from clogged sweat glands due to hot, humid conditions, and too much sun can cause excessive sweating which then leads to the development of a heat rash

Why am I suddenly allergic to the sun?

Sudden sun allergy, or photosensitivity, can be caused by changes in medication, exposure to certain chemicals, or developing conditions like polymorphous light eruption (PMLE).

Can sun poisoning lead to skin cancer?

Severe sun poisoning can increase your risk of developing certain skin cancers later in life. This is because sun poisoning arises when UV radiation severely damages skin cells and suppresses the immune system. This cellular damage can lead to genetic changes that cause those cells to grow out of control and turn into skin cancer.

Will my skin go back to normal after sun poisoning?

For mild sun poisoning, the skin typically heals back to normal within a few weeks. Severe cases can cause longer-lasting pigmentation changes, scars, wrinkles, and skin thinning that don't fully heal, but the skin does significantly repair itself over 2-3 months.

What is the difference between a sun rash and a sun allergy?

A sun rash is a reaction to sunlight, often related to sun poisoning. A sun allergy is an immune reaction to sunlight, usually with milder symptoms, and caused by external factors making skin sensitive. Both cause red, irritated skin when sunlight triggers a reaction.

What cream is good for an itchy rash?

Good creams for itchy rashes include over-the-counter hydrocortisone to reduce inflammation and antihistamines to relieve itching. Non-medicated calamine lotion, colloidal oatmeal, and cool compresses also soothe itchy rashes without irritating sensitive skin.

What skin rash can be mistaken for heat rash?

There are a few types of rash that can be mistaken for heat rash.

Contact dermatitis from plants, jewelry, clothing, or irritants can cause a red itchy rash resembling a heat rash.
Insect bites and stings can also mimic heat rash.
Eczema flare-ups and fungal infections like candidiasis or tinea versicolor may be mistaken for heat rashes.

Is aloe vera good for heat rash?

Aloe vera is an excellent home treatment for heat rashes. The cooling gel from the aloe plant reduces inflammation, speeds healing, and provides a soothing coating over the rash to calm pain and itching. Its antimicrobial properties can also prevent infection in broken blisters.

How can I reduce my child’s risk of heat rash during the summer months?

Frequently change diapers and damp clothes, use moisture-wicking fabrics, and keep skin dry. Also, make sure to limit time spent outdoors during peak sun hours, and avoid activities causing heavy perspiration to prevent heat rashes.

What should I do if sun poisoning symptoms don’t improve?

See a doctor if severe blistering, high fever, low blood pressure, extreme pain and discomfort, dehydration, or other sun poisoning symptoms don’t improve. The persistence of severe symptoms indicates complications that may require medical attention.

Do tick bites resemble sun or heat rash?

Sometimes tick bites can resemble mild heat or sun rashes with red, itchy bumps and skin irritation, but tick bites tend to occur sporadically, not across larger areas. Check for a tick embedded in the skin.

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