Heat rash, medically known as miliaria, is very common in warm and humid climates. Although children and infants are more susceptible to miliaria, it can affect people of all ages and genders (1). There are a few main causes that cause heat rash in adults. Depending on its type, this type of rash can be inflammatory or non-inflammatory. In this article, we discuss the causes, types, and symptoms of this issue, along with the heat rash treatment and management options available for adults. Keep reading!
What Is Heat Rash?
Heat rash is known by many names, such as eccrine miliaria, prickly heat, and sweat rash. It is a common skin issue that occurs when the eccrine sweat glands and ducts are blocked (1).
The eccrine sweat glands produce a majority of the body’s sweat. These glands can be found in the skin all over the body. When these sweat glands are blocked, the sweat produced is sent back into the dermis or epidermis layer of the skin. This causes a heat rash under the skin.
Prickly heat causes discomfort, nocturnal restlessness, and daily irritation (2). It can also lead to serious medical issues like impetigo, folliculitis, and furunculosis.
This condition is most commonly noticed during summer and is associated with a high fever. So what causes the eccrine glands in the skin to clog? There are three main causes that you can learn about in the next section.
Causes Of Heat Rash
Type 1 Pseudohypoaldosteronism is a condition where excessive amounts of sodium are released from the body, leading to its deficiency. One of the ways sodium is released is through the sweat glands. This condition has been associated with a type of miliaria known as rubra (1).
A rare autosomal recessive disease known as Morvan syndrome also leads to hyperhidrosis (excessive sweating), which may cause heat rash (1).
Certain medications can cause your body to sweat excessively, leading to heat rash. Bethanechol, clonidine, and neostigmine have been known to cause miliaria. In some cases, isotretinoin may also cause heat rash (1).
Bacteria like Staphylococcus epidermidis may cause blockages in the eccrine glands. These bacteria form biofilms that clog the glands, causing sweat to seep into the epidermis or dermis. This leads to overhydration, swelling, and further blockage of ducts. If left unmanaged, it can lead to the rupture of these glands and ducts (1).
Tight clothes, strenuous physical activity, and drug patches may also cause blockages in the eccrine sweat glands. Excessive sweating leads to overhydration of the stratum corneum, which leads to blockages. Also, it is common to sweat excessively in hot and humid conditions (1).
Some ducts become dilated under pressure, leading to their eventual rupture, which causes sweat to clog the skin. In some cases, UV ray exposure may cause damage to epidermal cells, which leads to duct rupture (1).
All of these causes can lead to three different types of heat rash, namely miliaria crystallina, rubra, and profunda. Learn more about them in the next section.
Different Types Of Heat Rash (Miliaria)
- Miliaria Crystallina: This type of heat rash occurs when the ducts of the stratum corneum (outermost layer of the skin) are blocked. They form vesicles (small liquid blockages) in the ducts (1).
- Miliaria Rubra:This type of heat rash occurs due to a blockage in the ducts of the epidermis at the subcorneal layers (the layer below the topmost layer of the skin). It may form spongiosis (spaces in the skin that mimic a sponge), leading to blockages. It can cause inflammation around the blocked ducts (1).
- Miliaria Profunda:Blockages in the papillary dermis (between the dermal and epidermal layers) lead to this type of heat rash. It may also cause spongiosis of the eccrine duct, similar to miliaria rubra. It leads to the rupture of the eccrine duct paired with significant inflammation (1).
Each of these types has specific characteristics or symptoms to help you distinguish between them. Keep reading to learn more about them.
Symptoms Of Heat Rash
- Miliaria crystallina appears as 1 to 2 mm superficial vesicles. The vesicles look like water droplets on the skin that are about to erupt. The rash usually appears within a few days of exposure to a trigger and resolves within a day after the superficial layer of skin sheds (1).
- Miliaria rubra is the most prevalent form of miliaria and may exhibit large red papules and vesicles (1). If pustules are present, then miliaria rubra is called miliaria pustulosa, and it may be a sign of a bacterial infection. It may lead to inflammation such as pain and itching, which could worsen because of sweat.
- Miliaria profunda shows up as firm, large, flesh-colored papules that are not centered around the follicles (1). These papules may be very itchy or not itchy at all.
Common symptoms to look out for include:
- Excessive sweating
- Clogged and sweaty skin
- Sponge-like spaces on the skin
- Sticky skin
- Burning sensation
Now that you know the causes and symptoms of heat rash, keep reading to learn how each of these types of heat rashes affects adults.
Heat Rash In Adults
- Miliaria crystallina affects both adults and infants, usually younger than 2 weeks old. The upper trunk, neck, and head are the most commonly affected sites (1).
- In adults, miliaria rubra is most likely seen in places where clothes rub on the skin, such as the trunk and extremities. The face is usually spared (1).
- In miliaria profunda, the rash distribution in adults mainly involves the trunk, but the arms and legs may also be affected. The skin rash usually appears within minutes to hours of perspiration and resolves within an hour after you stop sweating (1).
Identifying miliaria requires a thorough clinical diagnosis. Find out how it is diagnosed in the next section.
Diagnosis Of Heat Rash
In most cases, lab tests are inconclusive. However, dermoscopy is sometimes used to diagnose miliaria in people with dark skin. Some doctors may also recommend a skin punch biopsy to determine if you have a heat rash.
It is important to get the right diagnosis from a doctor as this condition may cause serious complications like anhidrosis (little to no sweat), leading to heat exhaustion and decreased thermoregulation in the body. This could have a permanent effect on your health.
This skin condition also causes changes in the epidermal layer, which could lead to bacterial infections.
Check out the next section for some treatment and management options you should follow to steer clear of and reduce heat rash.
Treatment And Management Options
Miliaria crystallina usually resolves on its own within 24 hours. And the miliaria rubra treatment focuses on reducing inflammation. Mild to mid-potency corticosteroids, like triamcinolone 0.1% cream, may be prescribed for one to two weeks (1).
Topical antibiotics, such as clindamycin, can treat any bacterial infections caused by miliaria pustulosa. The combined use of oral isotretinoin (40 mg per day) for 2 months and topical anhydrous lanolin may be effective in reducing miliaria profunda (1).
Besides these medical treatments, you can follow a few tips to treat and prevent heat rash:
- This skin issue can be treated with antibiotic, antimicrobial, and steroidal agents (3). Topical lotions, powders, gels, and ointments (containing a cleaning agent) may also be used. The cleansing agent removes all impurities from the skin to prevent any clogging.
- Soothing, anti-inflammatory, antipruritic, and cooling agents may also be prescribed.
- Natural remedies like an oatmeal bath, aloe vera massage, baking soda paste, sandalwood powder, Fuller’s earth, margosa leaves, and gram flour can be used to soothe heat rash.
- Miliaria rubra is generally reversible and responds immediately to cooling measures such as air conditioning, gentle breeze from a fan, or removal of excessive clothing.
- Supplemental vitamin C may help restore normal sweating in stubborn cases.
- Lightweight, soft cotton clothing is advisable for summer wear, as cotton is very absorbent and keeps moisture away from the skin.
- Exfoliate the skin to remove any blocking substances such as sweat, dirt, and product residue.
- Remove bandages or patches that could lead to sweat clogging. You should also treat febrile illnesses to prevent any risk of heat rashes.
Note: Topical agents such as powders, creams, and ointments (that are formulated for treating heat rash) are usually ineffective and may exacerbate a heat rash by keeping the skin warm and further occluding the pores.
The Bottom Line
Heat rashes are caused when your sweat glands are blocked. This leads to a sweat build-up in the top layers of the skin. These blockages may be caused due to ductal ruptures, excessive sweating, bacteria, and other risk factors. Wearing tight clothes can also lead to this issue. There are three types of miliaria (heat rash) that have characteristic features to help you tell them apart. Scroll up to read through the treatment options to help soothe and reduce heat rashes.