Contact allergy (poison ivy, nickel, soaps)

Medications

Chemicals

Immunocompromised individuals

TB skin test reaction (hardening at injection site)

Autoimmune disease (multiple sclerosis, rheumatoid arthritis, type I diabetes, psoriasis)

Delayed hypersensitivity reaction (rash, eczema, inflammation)

Guo, L. (n.d). Contact Dermatitis What Is It, Causes, Signs, Symptoms, and More. Osmosis. https://www.osmosis.org/answers/contact-dermatitis

Marwa , K., & Kondamudi , N. P. (2023, August 12). Type IV hypersensitivity reaction. National Center for Biotechnology Information. https://pubmed.ncbi.nlm.nih.gov/32965899/#:~:text=A%20Type%20IV%20hypersensitivity%20reaction,and%20neutrophils%2C%20can%20be%20involved.

Mayo Clinic Staff. (2023, April 25). Contact dermatitis. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/contact-dermatitis/symptoms-causes/syc-20352742

Novak-Bilić, G., et al. (2018, Dec). IRRITANT AND ALLERGIC CONTACT DERMATITIS - SKIN LESION CHARACTERISTICS. Acta clinica Croatica, 57(4), 713–720. https://doi.org/10.20471/acc.2018.57.04.13

Patel, K., Nixon, R. (2022) Irritant Contact Dermatitis — a Review. Curr Derm Rep 11, 41–51 . https://doi.org/10.1007/s13671-021-00351-4

Rogers, J.L,(2023). McCance & Huether’s Pathophysiology: The Biologic Basis for Disease in Adults and Children, Ninth Edition. Elsevier.

Vmc. (2005, October 11). Type IV hypersensitivity reaction information: Myvmc. HealthEngine Blog. https://healthinfo.healthengine.com.au/hypersensitivity-reaction-type-iv

T cells cause an inflammatory reaction against exogenous or endogenous reactions. Once there is an antigen exposure an immune and inflammation response is activated that calls for leukocytes. Macrophages and monocytes engulf the antigen which is presented to the T cell, which then becomes activated. These cells can result in illness because of what they release.

Initial exposure to an allergen or irritant triggers the sensitization phase. The allergen or irritant penetrates the skin barrier and interacts with antigen-presenting cells, such as Langerhans cells in the epidermis, which process and present the antigen to T cells.

Upon recognition of the antigen, naive T cells differentiate into effector T cells, mainly T helper 2 (Th2) cells. Th2 cells release pro-inflammatory cytokines, such as interleukin-4 (IL-4), interleukin-5 (IL-5), and interleukin-13 (IL-13), which promote the recruitment and activation of other immune cells.

Effector T cells and recruited inflammatory cells, including eosinophils, mast cells, and neutrophils, release cytokines and chemokines, leading to local inflammation. Mast cells play a crucial role by releasing histamine, which contributes to vasodilation and increased vascular permeability, resulting in erythema, edema, and pruritus.

Persistent exposure to the allergen or irritant and the release of inflammatory mediators cause tissue damage and disruption of the skin barrier. This leads to further infiltration of immune cells and exacerbates inflammation.

In most cases, removal of the offending substance and supportive care lead to resolution of contact dermatitis. However, sensitized memory T cells may persist in the skin, leading to a faster and more vigorous immune response upon re-exposure to the allergen or irritant, resulting in a more rapid onset of symptoms.

Signs and symptoms of contact dermatitis include redness, itching, swelling, and sometimes blisters or rash formation at the site of contact with the irritating substance or allergen.

Contact dermatitis is typically treated with topical corticosteroids to reduce inflammation and relieve symptoms. Using emollients to soothe the skin, and in severe cases, oral antihistamines may be prescribed for itching.

Young people are at higher risk for contact dermatitis due to their high skin turnover rate. Women are also more susceptible. Genetics may play a small role in predisposing one to contact dermatitis.

Irritants and allergens cause immune responses that damage the epidermis. Common irritants include solvents, rubber gloves, detergents, fertilizers, pesticides. Common allergens include nickel, antibiotic creams, poison ivy, insecticides, and cosmetics.

To prevent contact dermatitis, avoid touching irritants, wear protective gloves, wash your skin, use barrier cream, and apply moisturizer. Outdoor pets may also carry allergens from plants on their fur.

Irritant contact dermatitis is the most common occupational skin disease. In this form of contact dermatitis, keratinocytes trigger an inflammatory response. Being young, female, and having a Filaggrin loss-of-function mutation increase one's susceptibility to irritant contact dermatitis (Patel, 2022). You can avoid irritant contact dermatitis by using appropriate PPE and regularly applying barrier cream.

In allergic contact dermatitis, skin lesions are caused by a T cell mediated immune reaction. Research suggests that abnormalities in the skin's microbiome can contribute to the development of allergic contact dermatitis.