A form of radiation that is not visible to the human eye. It’s in an invisible part of the “electromagnetic spectrum” that reaches the earth from the sun. It has the UVA, UVB and UVC wavelengths that are shorter than visible light and invisible to naked eye 
Diverse types of interactions between organisms. Biological stressors can result from parasitism, competition, herbivory or predation 
These stressors are associated with excessive or reductions of temperature, solar radiation, moisture, among others 
Environmental psychodermatology is a developing area that studies the interaction between stressors, skin and the environment
Ozone Layer Depletion and Skin Cancer
The ozone layer is an area of the stratosphere (upper atmosphere, 25–35 km altitude), which has a high concentration of ozone. It’s a basic bio-protective filter that absorbs the solar radiation . About 98 % of the ultraviolet radiation of high frequency emitted by the sun is absorbed. Without this layer of human life on our planet would be virtually impossible to achieve (Fig. 5.1).
Diffuse exanthema in a patient with Zika virus (Courtesy of Dr Renata P. N Módolo)
There are many external (exogenous) factors that influence the health of the skin. These factors are determined by the environment that surrounds us, our overall health and lifestyle choices we make.
The ozone layer is a basic bio-protective filter that absorbs the solar ultraviolet radiation . The ozone-layer depletion occurs when chemical substances containing chlorine and bromine are emitted to the atmosphere. Since 1980, a sustained depletion of stratospheric ozone levels is occurring. The depletion of this important layer leads to increase of Ultraviolet levels in the environment, [7, 8] UV radiation causes deleterious effects on cells producing direct and indirect DNA damage, leading in mutagenesis in skin cells, leading to skin cancers . Skin cancers can cause functional damage and disfigurement (For more information, see Chap. 10).
UV Radiation and Premature Biological Aging of the Skin
Skin is under daily UV explosion. UV radiation explosion can cause acute or chronic harmful effects on the skin . Solar and UV radiation causes cellular and molecular damage that results in histopathologic and clinical degenerative changes that causes photosensitivity and photo-aging . Sunburn and tanning are the acute and reversible effects of the UV radiation on skin. While the chronic effects include immunosuppression, skin cancer and premature aging of the skin [11, 12]. Skin aging is characterized by formation of wrinkles and lines, loss of firmness and elasticity, increased pigmentation, and dull skin . Skin aging can cause significant psychological distress for many individuals leading to social anxiety and isolation (For more information, see Chap. 4).
Insects, Environment and Skin
Insects dominate all terrestrial environments . They play a crucial role in functioning of natural ecosystems and biogeochemical cycling of nutrients [14, 15]. They are human’s competitors for natural resources, food and fibers. Although insects are part of a natural system that provides environmental stability they can also transmit many diseases that affect plants, domestic animals and humans [14, 16]. They have the capacity of spreading diseases caused by different types of bacteria, protozoans and viruses. The most common diseases caused by insects and their cutaneous manifestations are presented in the Table 5.2.
Most common diseases caused by insects and their cutaneous manifestations
Aedes aegypti and Aedes albopictus mosquitoes
Confluent erythema, morbilliform eruptions, and hemorrhagic lesions 
Aedes aegypti and Aedes albopictus
Skin rash, apthae like ulcers, pigmentary changes, desquamation, exacerbation of the existing dermatoses 
Urticaria, angioedema, reticulated blotchy erythema with petechiae 
West Nile virus
Genus Culex mosquitoes (most common)
Generalized, maculopapular rash, dysesthesias, pruritus 
Culex, Anopheles and Aedes mosquitos (most common vectors)
Edema with thickening of the skin and underlying tissues, rashes, urticarial papules, and arthritis, hyper- and hypopigmentation macules, chronic ulceration, epidermal and sub-epidermal nodules, and clinical intertrigo 
Phlebotomine Sand flies
Skin and mucosal ulcers 
Swelling and/or redness at the skin infection site 
Environmental Pollutants and the Skin
The skin acts as a barrier between the organism and environment and is constantly exposed to environmental pollution. Different types of pollutants can come into contact with skin through inhalation, ingestion or topically. Pollutants become toxic to vital organs after metabolization, accumulation or activation and are related to a genotoxic effect.
Ultraviolet radiation, described before, can be considered a “physical pollutant” and is responsible for skin cancers .
Volatile organic compounds such as benzene is another widely distributed environmental contaminant that has cutaneous absorption and is also present in the air, food. Intoxication by benzene can cause leukemia [25, 26]. Benzo[a]pyrene induces oxidative stress in the skin inducing skin cancer and inflammatory skin diseases . Heavy metals, another common environmental pollutant, can also be absorbed by skin and cause systemic diseases. These metals are more commonly found in petrol, soil and industrial effluents . One example that has a correlation with skin diseases is the arsenic. Jarup explains that long-term exposure to arsenic in drinking water is related to hyperkeratosis, pigmentation changes as well increased risks of skin cancer . In addition, environmental cigarette smoke, another oxidizing agent, is related with androgenetic alopecia .
Air Pollution is also responsible for skin aging. Research has shown that air pollution exposure can cause pigment spots and wrinkles. These pollutants break the collagen fibers in the skin and disrupt the lipid layer, impairing the skin barrier function and leading to aging. Some examples of air pollutants include smog, dust, cigarette smoke, and car exhaust. An anti-pollution daily skin care may be helpful to minimize the damage caused by air pollution exposure and should include regular wash of the face, use of oral and topical antioxidants and a balanced diet .