Definition

Miliaria crystallina, or prickly heat, is a condition where sweat gets trapped under the skin. Miliaria is common in newborns (2 weeks of age or less), but can also occur in adults (especially those who have recently moved to a warmer climate). Miliaria has four types depending on the depth of the sweat gland blockage, namely:

• Miliaria crystallina. This is the mildest type of miliaria. It occurs when the openings in the sweat glands and ducts (pores) become blocked. It is characterized by small, clear, water droplet-like vesicles that are easy to break.
• Miliaria rubra. This type of miliaria occurs in the deeper parts of the skin. Signs and symptoms include small reddish papules that become inflamed, accompanied by itchiness and pain.
• Miliaria pustulosa. This is when the papules and vesicles in the miliaria rubra are filled with pus.
• Miliaria profunda. This type of miliaria affects the deep layer of the skin (dermis). It causes stiff, painful, and itchy papules due to inflammation. They can resemble standing hairs and may burst.

Causes

Miliaria can impact individuals of all ages and genders, but newborns and children are more susceptible because of their underdeveloped sweat glands and ducts. The causes of miliaria crystallina can include the following:

• Agents that occlude the skin. These may consist of tight clothes and transdermal medicine patches.
• Pseudohypoaldosteronism type 1 (PHA1). The body is resistant to the hormone that controls mineral levels in the body. Therefore, a lot of sodium is excreted through sweat, so the amount of sweat also increases.
• Morvan syndrome. This hereditary condition leads to hyperhidrosis, resulting in an increased susceptibility to developing miliaria.
• Certain medicines. Bethanechol, clonidine, and neostigmine are medicines that can cause miliaria, a skin condition characterized by sweat-induced rashes. Additionally, isotretinoin is another medicine that can induce miliaria. 

Risk factor

Factors that increase the likelihood of developing miliaria crystallina include:

• Newborns, because their sweat glands and ducts are still developing 
• Residing in a region with a warm and humid climate 
• Active person who likes to exercise 
• Experiencing prolonged bed rest and fever 

Symptoms

Miliaria crystallina presents as transparent vesicles with delicate layers. They are named crystallina (crystal-like) because they resemble water droplets. They sit on the skin's surface, typically causing no inflammatory reaction. They are typically located in skin creases or areas where the skin comes into contact with clothing in adults. Infants typically have these skin lesions on their neck, shoulders, and chest. They are also present in the axillae, elbow folds, and inguinal region. They typically manifest a few days following heat exposure and resolve within a few days. This occurs due to the shedding of the dead outer layer of the skin.

Diagnosis

Physicians can diagnose miliaria by asking about your medical history and examining the rash and lesions on your skin. Typically, doctors may diagnose this illness without requiring any specific testing. The cytology technique for miliaria crystallina does not show signs of inflammation or infection in the cells from skin lesions fluid. During tissue examination, the doctor may identify blockage of the sweat glands and ducts in the outer layer of the skin.

Skin inflammation may suggest the existence of more severe forms of miliaria, such as miliaria rubra, pustulosa, and profunda.

Management

Risk factors for miliaria crystallina include hot and humid settings. The main preventive measure is to minimize sweating and prevent blockage of the sweat glands and ducts. This may involve:

• Engaging in activities in colder climates
• Wearing loose, lightweight clothing that promotes the skin to breathe
• Exfoliating the skin (removing dead skin cells)
• Avoid using items that can occlude the skin, such as plasters, bandages, and patches
• Treating fever
• Avoid excessive physical exertion in hot conditions until the miliaria rash improves 

Miliaria crystallina typically cures on its own within 24 hours after the afflicted skin layer sheds, requiring no specific treatment. You can also use cooling agents such as lotions containing calamine or menthol, as well as cold compresses. These agents can help cool down the skin more quickly. Other agents, such as lanolin can also be used to prevent blockage of the sweat gland ducts, allowing sweat to flow smoothly to the skin surface. You can bathe twice a day using an adequate amount of soap.

Antibiotics are unnecessary for miliaria crystallina because this condition typically does not lead to inflammation or bacterial infection. Antibiotics are typically prescribed for miliaria pustulosa. Furthermore, administering anti-inflammatory medications like corticosteroids is unnecessary, as this kind of miliaria typically does not include inflammation.

If the aforementioned remedies aren't helping your situation, you may wish to contemplate relocating to a colder location.

Complications

Miliaria typically resolves without leaving any lasting marks. Individuals with dark skin tones are more susceptible to developing patches that are either lighter or darker than their natural skin hue. This occurs as a response to skin inflammation. This discoloration typically resolves within a few weeks to months. Another potential complication is bacterial infection of the sweat glands, leading to painful and itchy vesicles filled with pus. Possible consequences may involve impetigo or abscesses developing on the skin. 

Heat intolerance is another potential complication. This condition is defined by anhidrosis (inability to sweat) in the affected skin, along with weakness, fatigue, dizziness, and fainting. Moreover, it can hinder an individual from engaging in a job or physical activity. This condition is more prevalent in miliaria profunda.

Prevention

Take the following measures to prevent miliaria crystallina:

• During hot weather, it is advisable to wear loose and lightweight clothing to prevent excessive dampness on the skin. Infants should avoid wearing multiple layers of clothings
• Limit physical activity during periods of high heat. It is advisable to seek shelter behind trees, or stay indoors with controlled temperature. Additionally, fans can be used to promote air circulation in the room
• Maintaining a cool and well-ventilated bed
• Avoid using ointments and creams that may clog skin pores
• Applying sunscreen
• Avoid drugs known to induce perspiration, such as clonidine, beta blockers, and opioids.
• Before exercising, you can use lanolin to prevent the occurrence of new prickly heat. 

When to see a doctor?

Miliaria crystallina typically gets better by cooling the skin and avoiding heat exposure. Visit a medical professional if you or your child experience symptoms that last for more than a few days, or if the symptoms of prickly heat worsen or seem to be getting infected.

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