General introduction and allergy reactions

The skin consists of two components -- the epidermis and the dermis, these layers are separated by a basement membrane. The epidermis consists of five strata: the stratium corneum, stratium lucidum, stratium granulosum, stratium spinosum and stratium basale.The outer most layer of the epidermis is the stratium corneum, it's main purpose is to form a barrier to protect underlying tissue from chemicals, toxins and mechanical stress, this makes it a very important constituent of the skin.
Image 1: Structure of the Skin

Skin is the body's first line of defense against external insult; the skin is rountinely exposed to various chemical agents that may damage the skin layer and overwhelm it's protective function causing chronic or acute reactions/ injury to the skin.

However this doesn't happen very often as the skin doesn't just repel toxic agents but reacts with them in a variety of complex defensive mechanisms such as thermal and electrolyte regulation to prevent internal or widespread cutaneous damage. The skin absorbs exogenous substances thorough a process called percutaneous absorption and only small amounts of toxins are able to penetrate the stratium corneum layer, however sometimes even a small amount of a potent toxin can cause extensive damage and allergic skin reactions.

Toxic response of the skin can be triggered on exposure to a wide array of chemicals including cosmetics, hair dyes, metals and even dental materials. Most common toxic responses of the skin include dermatitis (rash), swelling, dryness and erythema. Cosmetics and other everyday products like toothpaste,shampoo, and deodorant are known to contain toxic chemicals that may induce more serious skin conditions like eczema, psoriasis and comedogenic acne. Some of these chemicals may also cross-react with each other causing skin toxic responses, these include paraben preservatives that are present in most cosmetic products and phenylenediamines -- hair dye ingredients.

Acne and other chemically triggered skin conditions:

Some of the common chemicals that we come into contact with everyday, are able to induce skin conditions such as comedogenic acne and even eczema.

pcongestion.jpgComedogenic acne is characterized by a comedone which may be open or closed, additionally some papules, pustules and cysts may be present.

Image 2: Open and closed comedone formation in acne.

Acne is triggered by chemicals that penetrate the skin and get into the hair follicle and
clog pores; toxins like this include various oils and fragrances. Acne can be treated with topical antibiotics and a compound called benzoyl peroxide.

Image 3: Comedogenic acne on the cheeks and nose.
Chemically induced eczema is characterized by the inflammation or irritation of the epidermis that manifests as a rash. The amount of skin involved may vary from a single small lesion to widespread large areas all over the body and it is usually triggered by cosmetics, toiletries and fragrances. There is no known cure for eczema; the main therapeutic agents used are corticostreroids and the treatments are aimed to control the symptoms by reducing inflammation.


Source: 4: Eczema on the foot.

Other chemicals, and medications can induce a more serious skin condition -- psoriasis. Psoriasis is a common and one of the most persistent of skin disorders. It's characterized by skin cells that multiply much faster than normal. As underlying cells reach the skin's surface and die, the sheer volume of dead cells causes raised, red plaques covered with white scale.
Psoriasis can be influenced by various chemicals as well as drug intake. Drug ingestion may result in both the exacerbation of pre-existing psoriasis, and the induction of psoriatic lesions. The most common causative agents for drug-induced or drug-aggravated psoriasis are beta-blockers, synthetic antimalarial drugs, non-steroidal anti-inflammatory agents, and antibiotics such as tetracyclines. Psoriasis is un-curable but with appropriate treatment its possible to clear up the lesions within a few months, all psoriasis treatments are aimed at slowing the growing rate of skin cells.

Image 5: Psoriasis vs Normal Skin.

Test your knowledge of chemically induced skin conditions here:

Answers to MCQ:

General introduction and allergy reactions:
Acne and other chemically triggered conditions:
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