Article by the experts: Kouassi et al.
The skin, the human body’s largest and heaviest organ, is composed of three layers: the epidermis, dermis, and hypodermis. It serves multiple functions including protection, temperature regulation, sensation, immunity, and mechanical behavior. The skin also acts as a barrier between the body and the external environment, protecting against various physical, chemical, and biological factors that can cause skin damage.
Ultraviolet (UV) radiation, a natural component of sunlight, is categorized into UVA (315–400 nm), UVB (280–315 nm), and UVC (100–280 nm). However, UVC is entirely absorbed by the atmospheric ozone, allowing only UVA and UVB to reach the earth’s surface and penetrate the skin at varying depths. UVA rays penetrate the deep layers of the dermis, while UVB rays are primarily absorbed by the epidermis. UV radiations are the primary cause of skin damage, including sunburns, skin cancers, and photo-aging.
Chronic exposure to UV is linked with skin burns, predominantly caused by UVB rays. These burns are classified into three categories: first, second, and third-degree burns, in ascending order of severity. The classification of these burns depends on the ultraviolet index, the skin phototype, and the duration of sun exposure. The most common types of skin burns are first-degree burns, such as erythema, which results in varying degrees of skin redness. Overexposure to UV radiation can lead to DNA damage, including mutations or chromosomal rearrangements.
Bacteria, which are single-celled organisms from the prokaryote kingdom, can inhabit various ecological niches, including the human skin and body (such as the intestines and respiratory tract). The human skin is home to a diverse range of microorganisms, including bacteria, viruses, and fungi, collectively known as the microbiota. The composition of this microbiota depends on the skin’s physiology, such as whether it’s moist, dry, or sebaceous.
Bacteria are the most prevalent, followed by fungi and viruses. The skin microbiota includes various bacterial species like Staphyloccocus, Corynebacterium, and Cutibacterium. These bacteria can either be commensal, providing beneficial protection against pathogenic bacteria, or they can be pathogens themselves, causing various skin infections.
Common bacterial skin infections include impetigo, cellulitis, erysipelas, folliculitis, and furuncles. Impetigo affects the epidermis, while cellulitis and erysipelas are deeper infections reaching the dermis. Folliculitis and furuncles are infections of the hair follicle. These skin conditions are primarily caused by two pathogenic bacteria: Staphylococcus aureus and Streptococcus pyogenes. Staphylococcus aureus is also linked to atopic dermatitis (eczema), and acne, a skin condition affecting the pilosebaceous follicles, is caused by the pathogenic bacterium Cutibacterium acnes.
Chemicals are another risk factor that can cause skin injuries, particularly inflammatory skin diseases. People can be exposed to chemicals in various workplaces, including cosmetology, health care, agriculture, manufacturing, painting, and construction sectors. Chemical exposure can also occur through the use of consumer products like cosmetics and household items. Among the different classes of chemicals (fragrances, dyes, surfactants, preservatives/biocides, solvents, metals), fragrances and preservatives are the most common culprits of skin lesions. Examples of chemical allergens include fragrances like hydroxycitronellal and geraniol found in perfumes, and linalool, limonene, and citronellol used in hygiene products and daily moisturizers. Preservatives like formaldehyde, isothiazolinones, and quaternary ammonia compounds, used in cosmetics (facial skincare products, body lotions, deodorants, shampoos, liquid soaps, and detergents) are also common allergens.
Chemical-induced skin damage can result in conditions like irritant contact dermatitis and allergic contact dermatitis. Typical symptoms of dermatitis include itching, pain, redness, swelling, and dry, scaly skin that may develop cracks.
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