Environmental factors that explain the increase in the prevalence of atopic eczema in the population.

Although it is closely linked to genetics, atopic dermatitis is influenced by several environmental factors. These factors play a significant role in triggering eczema flare-ups. Therefore, changes in our lifestyle that lead to an increase in these environmental factors also cause a rise in the prevalence of atopic eczema. Some of these factors include:

• Enhanced hygiene.

  Formulated in 1989 by David STRACHAN, a university researcher, the hygiene hypothesis is based on the assumption that a reduction in early childhood exposure to infections and microbial components in industrialized countries leads to a decrease in the maturation of the immune system and, consequently, an increase in the prevalence of allergic, autoimmune, and inflammatory diseases, such as eczema. However, while evidence has indeed been established in epidemiological studies within industrialized countries, the hygiene hypothesis has its limitations and the hygiene factor does not account for the increase in the incidence of atopic eczema in less developed countries.

• An increasingly urban lifestyle.

  According to the United Nations (UN), the global urban population is rapidly increasing, while the growth of the global rural population is slowing and is expected to decline from 2030 onwards. In 2018, the UN estimated that 55% of the world's population lived in urban environments, up from about 40% in 2000. However, a study has shown that individuals living in urbanized environments are more prone to atopic eczema than others. Pollution, a factor that exacerbates outbreaks of eczema, is notably responsible for this.

• Still high levels of smoking.

  Smoking is a risk factor for the development of atopic eczema due to the irritating and polluting substances contained in a cigarette. These compounds easily penetrate the fragile skin barrier of atopic skin and trigger immune responses that lead to eczema flare-ups. However, despite an increasing number of prevention campaigns, the number of smokers worldwide is not decreasing, which contributes to the rising prevalence of atopic eczema.

• The increasing stress.

  Several scientific studies have demonstrated that there is a link between eczema and stress. Various mechanisms are at work, among which is the reduction of lipid synthesis in the stratum corneum mediated by the cortisol, the stress hormone. The skin barrier, already fragile in atopic skin, becomes even more diminished.

  Indeed, stress is becoming increasingly prevalent in the world and is part of a constant state of dissatisfaction. Sociologists observe that individuals today seem to expect more from life than previous generations, which pushes them to set ambitious goals. The desires for self-realization and personal achievement are growing but are sometimes accompanied by an unequal time management between personal and professional lives and a (too?) heavy work commitment, leading to significant stress. Grief, separations, worries about global economic, political, health, and climate crises are other stress-inducing factors.

• Climate change.

  Previously mentioned as a source of stress, climate change is also responsible for a general increase in average temperature. According to the Ministry of Ecological Transition, the annual global temperature has risen by nearly 1°C since the end of the 19th century. Individuals suffering from atopic eczema are sensitive to heat, which is a trigger for itching. Therefore, it is possible that the general increase in temperature has contributed to the rise in global prevalence of atopic eczema.