Heat rash: Symptoms, causes and treatment of prickly heat

Heat rashes, also called prickly heat and miliaria, are red, small, and raised spots that make you feel itchy. Right from children to adults, anyone can have heat rashes. These raised spots can pop up on different parts of the body, especially the scalp, chest, and the upper back. The skin condition mostly occurs during hot and sticky weather, and may lead to discomfort. You should go for cool baths and reduce exposure to heat to get some relief from the itching. Read on to know the symptoms of heat rash and simple ways to treat this skin problem.

What is a heat rash?

Heat rash is a skin condition caused by the blockage of sweat glands. When sweat gets trapped under the skin due to obstructed sweat ducts, it leads to the formation of rashes. These rashes are common in hot and humid conditions, where excessive sweating occurs, explains dermatologist Dr Mihika Noronha. They appear as raised spots, which are 2 mm to 4 mm across, and some of them may have fluid in them, according to the UK’s National Health Service.

There are three types of heat rashes, each varying in severity:

1. Miliaria crystallina

This is the mildest form of heat rash, which presents as clear, tiny blisters filled with fluid. The blisters are superficial and often do not cause much discomfort. Miliaria crystallina primarily affects the top layer of the skin and is more common in babies than adults, says the expert.

2. Miliaria rubra

Also known as prickly heat, miliaria rubra is more severe than crystallina. It is characterised by small red bumps that can cause intense itching and a prickling sensation. These bumps may sometimes be filled with pus, indicating inflammation. Miliaria rubra affects deeper layers of the skin and is the most common form of heat rash in adults.

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3. Miliaria profunda

This is the most severe type of heat rash and is less common than the other forms. Miliaria profunda manifests as deep, painful red swellings. It occurs when the sweat ducts in the dermis (the deeper layer of skin) are blocked, preventing sweat from reaching the surface. This type of rash can be more persistent and very uncomfortable.

What are the symptoms of heat rash?

The symptoms of heat rashes are primarily characterised by itchy rashes that appear over areas of the skin where sweat glands are present. The specific symptoms vary depending on the type of heat rash –

1. Miliaria crystallina

The symptoms include clear, tiny blisters that are typically not accompanied by significant discomfort or itching. The blisters may be fragile and break easily.

2. Miliaria rubra

This type is marked by small red bumps that may cause a prickling or stinging sensation. The affected areas are often itchy and may feel uncomfortable, especially when exposed to heat.

3. Miliaria profunda

The symptoms of this severe form include deep, painful red swellings. These swellings can be quite uncomfortable and may cause a lot of pain. The rash occurs when sweat is trapped deep within the skin, leading to inflammation and discomfort.

In general, all types of heat rashes are associated with itching, discomfort, and visible changes to the skin’s appearance, says Dr Noronha.

What are the causes of heat rash?

The main causes of heat rash include:

1. Excessive sweating

High temperatures and humidity, as well as physical activity, can cause excessive sweating. When sweat cannot escape due to blocked sweat ducts, it accumulates under the skin, leading to heat rashes.

2. Dead skin cells

The build-up of dead skin cells can block sweat ducts, making it difficult for sweat to escape, says the expert. So, you must exfoliate your skin once or twice a week to prevent build-up of dead skin cells.

3. Tight and non-breathable clothes

Wearing tight or synthetic clothing that does not allow the skin to breathe can trap sweat and contribute to the development of heat rashes. Non-breathable fabrics like polyester and nylon are particularly problematic, says the expert.

4. High fever

Fevers can increase the body temperature and lead to sweating, which may lead to heat rashes. This is often in the case of bedridden people.

Does heat rash spread to other parts of the body?

Heat rashes typically affect areas of the body where sweat glands are concentrated and where air circulation is limited. The most commonly affected parts of the body include:

• The scalp is prone to heat rashes, especially in people with thick hair or those who wear hats frequently, trapping heat and sweat.
• The chest is another common site for heat rashes, as it is often covered by clothing, leading to reduced air circulation and increased sweating.
• The upper back is susceptible to heat rashes due to its coverage by clothes and limited ventilation.

These areas are frequently covered and subjected to sweating, creating an ideal environment for sweat gland blockage and the development of heat rashes. They do not typically spread from one part of the body to another. However, they can appear in different areas simultaneously if the conditions that cause them—such as heat, humidity, and sweating—affect multiple parts of the body, says the expert. For instance, it is not uncommon for heat rashes to appear in the groin or elbow creases, especially in situations where sweat accumulation and friction occur.

How long does heat rash last?

The duration of heat rashes can vary, but most cases resolve within a few days. The key factors influencing the duration include the type of heat rash, the severity of the condition, and whether the individual continues to be exposed to the contributing factors.

• Miliaria crystallina: Typically resolves quickly, often within a day or two, as it is the mildest form and affects only the top layer of the skin.
• Miliaria rubra: May take a few days to clear up, especially if the person continues to be exposed to heat and humidity.
• Miliaria profunda: This severe form may take longer to heal due to the deeper involvement of sweat glands and the potential for inflammation. It can persist for several days or even weeks if not properly managed.

If the exposure to heat and humidity continues, heat rashes can persist or recur. Effective management and preventive measures are crucial for faster resolution and to avoid prolonged discomfort.

How to treat heat rash?

There are several ways to help alleviate the symptoms of heat rashes and promote healing:

1.Cool baths

Taking cool baths can soothe the skin and reduce itching and inflammation, says the expert. But avoid using harsh soaps, as they can irritate the skin further.

2. Calamine lotion

Applying calamine lotion to the affected areas can provide relief from itching and discomfort caused by heat rash. It has a cooling effect and helps to dry out the rash.

3. Emollients

Take help of a dermatologist for recommendations on emollients that will not clog pores. These can keep the skin moisturised without exacerbating the condition.

4. Avoid heat exposure

Stay in cool, and shaded areas, and avoid activities that cause too much of sweating. Use fans or air conditioning to keep your room cool. But don’t sit under a fan or in front of an AC when you are sweating, as you might catch cold.

5. Ice pack

Cool baths are good to get relief. You can also apply something cold, such as an ice pack or a damp cloth. While using an ice pack, wrap it up in a towel, and use it for about 20 minutes.

How to prevent heat rash?

Preventing heat rashes involves several strategies aimed at reducing sweating and improving skin ventilation:

• Opt for loose-fitting clothes made from natural fabrics like cotton or linen, which allow the skin to breathe and reduce sweat accumulation.
• Use fans or air conditioning to cool down the place you are in.
• Take cool showers after physical activity to wash away sweat and prevent the blockage of sweat ducts.
• For babies and bedridden patients, use breathable bedding materials instead of waterproof ones that can trap heat and moisture.

Heat rash, a skin condition common during summer, can cause discomfort. Stay in cool areas, and wear clothes made of breathable fabric to prevent heat rash. If you still get heat rash, and you find it accompanied by pain, pus discharge, or does not improve within a few days, see a doctor for further evaluation and treatment.