Introduction

Definition of skin rash

Skin rash is when the skin becomes red and inflamed with a bumpy texture. The skin may become dry, itchy, and painful. Dry skin may crack or blister due to the lack of moisture. Skin rash is a vague condition, and causes can vary from bacterial infection, atopic dermatitis (eczema), to allergic reactions.¹

Definition of contact dermatitis

 Contact dermatitis is a common type of skin rash that is a result of the body reacting to allergens or irritants that the skin is in contact with. This condition is classified under eczema as the skin becomes dry and irritated.² While atopic dermatitis is common in young children, contact dermatitis is mainly prevalent among adults. It is estimated to affect 15% of the adult population throughout their lifetime. The percentage incidence will depend on factors like demographics and occupational exposure.³ Importance of understanding causes and treatments

Contact dermatitis

Contact dermatitis is classified into two groups—irritant contact dermatitis and allergic contact dermatitis.² 

Irritant Contact Dermatitis (ICD)

Irritant contact dermatitis (ICD) is stimulated when the skin comes in contact with chemicals, soaps and solvents. Symptoms include red, dry, and cracked skin.⁵ The longer the duration of exposure and the higher the concentration of irritants, the more likely it is for ICD to develop.⁴ 

Upon contact with the irritant, a non-specific immune response is triggered, and inflammatory factors are released from epidermal cells. However, unlike in allergic contact dermatitis, T-cells (a type of immune cell that helps fight infections and allergies) are not recruited.⁵ Depending on occupational exposure, some workers are at higher risk of developing ICD. For example, hairdressers, chemical workers, and agricultural workers often work with irritants. Healthcare workers and cleaners are also at risk due to the use of soaps with strong chemicals.⁶

Allergic Contact Dermatitis (ACD)

In allergic contact dermatitis (ACD), when the skin comes in contact with allergens, the innate and adaptive immune responses are triggered, causing blisters and an itchy rash. Allergens can be metals like cobalt and nickel, poison ivy, dyes, and cosmetics.⁵ Factory and construction workers who are in contact with rubber, textiles, and strong glues are also at risk of developing ACD.⁶ 

CD4 and CD8+ T cells (immune cells that help fight infections) are stimulated to the affected site, causing inflammation. Antibodies will be subsequently released to destroy foreign invaders, like allergens.³ It has also been proven that natural killer cells (immune cells that attack infected or abnormal cells) are involved in the immune response in ACD. In a 2020 study, human skin biopsies were done after a nickel patch test was conducted in patients with nickel allergies. Results showed an increase in natural killer cell count, which can be used to distinguish ACD from ICD.⁷

Symptoms of contact dermatitis

The symptoms of contact dermatitis vary depending on the severity of the skin condition and the cause of it. Common symptoms include red and itchy rashes. The skin texture may become leathery and bumpy. Blisters filled with fluid may also form. In some cases, the skin may crack and be crusty due to dryness. Some patients may experience swelling or tenderness on their skin as a result of contact dermatitis.⁸

Diagnosis

One common diagnosis method is to perform a patch test on the patient’s skin. A series of potential allergens are selected and placed on the patch. The allergens are chosen based on the patient’s occupation, site of dermatitis, and their usual products that could be a potential cause of the skin condition. The patches are applied when the dermatitis is inactive for a more accurate diagnosis. The patients must also not consume any immunosuppressive agents or apply their steroid cream prior to the test. The outcomes are scored based on the degree of reaction to each allergen.⁹

 If further evaluation is necessary, a skin biopsy may be performed on the affected skin, although this procedure is uncommon. A small skin sample is taken and viewed under the microscope. The type of dermatitis is then diagnosed by a skin specialist.¹⁰

Prevention and treatment options

Identification and avoiding triggers

It is important to identify irritants or allergens that trigger skin rash. By doing so, contact and exposure to the trigger can be avoided. For instance, if certain soaps or beauty products are found to be responsible for one’s contact dermatitis, fragrance-free and soap-free cleaners or moisturisers can be used as an alternative.¹¹

Topical treatments

Corticosteroids (for inflammation)

The FDA has approved the use of topical corticosteroids for treating skin conditions like contact dermatitis. Its purpose is to reduce inflammation at the affected site. Corticosteroids directly cause vasoconstriction of blood vessels in the upper dermis, reducing the number of inflammatory mediators reaching the skin layer; it has an anti-inflammatory effect. They can come in many forms, including gels, creams, and ointments.

There are seven classes of potency of corticosteroids. Potency is defined as the dose of drug required to produce a certain therapeutic effect. Class I indicates the highest potency.¹² Although the use of topical corticosteroids is common for contact dermatitis, there are side effects like skin irritation, delayed wound healing, and collagen production. Hence, they should be used in moderation.¹³

Emollients (to moisturize)

In contact dermatitis, the skin barrier is destroyed, causing dry and scaly skin. Moisturisers are scientifically proven to protect the skin barrier, maintain skin hydration, and have anti-inflammatory effects. Emollients, a type of moisturiser, contain lipids and other components that improve skin softness, fluidity, and hydration. Other moisturisers like humectants and aloe vera gel differ in terms of their composition, but they generally have the same function.¹⁴ 

Medications

Antihistamines (for itching)

Medications may be prescribed to treat skin itching due to contact dermatitis. Hydroxyzine and cetirizine are recommended to control the symptoms of the skin condition.⁵ Antihistamines (drugs that reduce allergy symptoms) work by binding to histamine receptors. They are antagonists (blockers) of these receptors. The drug treats allergies and allergic rhinitis (inflammation of the nose due to allergies) by specifically targeting H1 histamine receptors expressed in nerves, vascular smooth muscle cells, and endothelial cells. Side effects of H-1 receptor antihistamines include dry mouth and dizziness, and these are more commonly seen in first-generation antihistamines.¹⁵

Immunosuppressants (for severe cases)

For severe cases, immunosuppressants may be prescribed. Examples of immunosuppressants include Azathioprine and Methotrexate. Systemic steroids are often used to treat severe cases of eczema (atopic dermatitis). They are used for the purpose of reducing inflammation. However, it is not highly recommended due to side effects like the reemerging of symptoms once the consumption of the medication is discontinued. This is known as the “rebound effect.” Other side effects include an increase in the risk of infections and high blood pressure.¹⁶

Complications

Secondary infections

Those with contact dermatitis are prone to developing secondary infections as there are open wounds on the skin due to constant scratching. The infection may be caused by Staphylococcus or Streptococcus bacteria. As a result, symptoms of contact dermatitis worsen. The skin becomes redder and more crusty. The patient may experience fever when the body is infected by bacteria. Antibiotics will be needed to treat the infection.¹⁷ 

Chronic dermatitis or eczema

If the symptoms of contact dermatitis persist and worsen over time, it can become long-lasting and chronic. This can be because there is a continued exposure to the irritant or allergen or the symptoms were left untreated.¹⁸

Scarring or pigmentation changes

Some patients may experience hyperpigmentation because of scarring of the skin and the inflammatory response. This is when there is a decolouration and darkening of the skin that is prominent after the patient is healed from this skin condition. The post-inflammatory hyperpigmentation may fade away, but many remain for many years. This phenomenon is also common in other skin conditions like eczema.¹⁹

Summary

By identifying the underlying causes and risk factors of contact dermatitis, preventive measures can be taken to reduce the risk of recurring skin rashes. The most effective treatment can also be recommended to patients to manage their respective symptoms while minimising the adverse side effects and complications. This would require the collective effort and collaboration between doctors, dermatologists, and nurses in patient education and symptom management.