Does tobacco have an effect on eczema?

The existence of a relationship between atopic eczema and tobacco is a recent discovery. Several studies have shown thatsmokers are associated with a high prevalence of atopic dermatitis. Similarly, although research results are mixed, researchers have found that atopic eczema is more common than average among people exposed to second-hand cigarette smoke.

• Active or passive smoking in pregnant women increases the risk of eczema in newborns: It is estimated that around 1.7% of women worldwide smoke during pregnancy. Research appears to suggest that prenatal exposure to passive smoking increases the prevalence of eczema diagnosis in children. While most studies assessing the effect of smoking and exposure to ambient tobacco smoke on health status rely on self-reports, a 2008 study was based on the concentration of cotinine in the cord and mother's blood, a metabolite of nicotine with a longer half-life (18 - 20 hours) than nicotine (1 - 2 hours). It was found that non-smoking women exposed to tobacco smoke had a high cotinine rate, and even more so, full-time housewives had higher cotinine levels than women in employment. The data demonstrated that exposure to passive smoke during pregnancy can play a role in the development of atopic dermatitis.

  However, studies have not yielded similar results with active maternal smoking during pregnancy or breastfeeding, pointing in different directions. Indeed, some studies have found no significant correlation between the risk of developing eczema in future babies and the mother's active smoking, and other researchers have found that smoking during pregnancy was associated with a low risk of eczema in the child. Further research is therefore necessary before definitive conclusions can be drawn. Despite the limited evidence, the results should be interpreted with caution, as the adverse effects of smoking during pregnancy have been widely demonstrated, particularly on the development of asthma in the child. Thus, the data suggest that pregnant women should minimise their contact with cigarette smoke to prevent the development of eczema in their offspring.

• Parental smoking is a risk factor in the development of eczema in children: In 2004, 40% of children worldwide were reportedly exposed to household smoke. There is a significant association between the degree of exposure to cigarette smoke and the prevalence of atopic eczema in children. A study determined the impact of passive parental smoking on atopic eczema, allergic sensitisation, and allergic respiratory diseases in 1,669 six-year-old children with and without parental atopy. The prevalence of eczema in genetically predisposed children was 28%.

• Smoking can exacerbate hand eczema, whether in a professional environment or in the general population: Hand eczema is a common condition in the general population and even more prevalent in high-risk professional environments (hairdressers, dental prosthetists, bakers, workers, etc.). Already favoured by all allergenic and irritating professional practices, tobacco would add an extra dose of irritation in patients suffering from hand eczema and would cause a delay in the restoration of the broken skin barrier in people with hand eczema. Although still contradictory, some studies have highlighted a positive association between daily smoking, and the increase in prevalence, frequency and severity of hand eczema. However, this negative influence of smoking on eczema can be reinforced in manual workers who are simultaneously exposed to irritants, mechanical trauma and work in a humid environment.

Most of the research conducted has shown that the association between smoking and eczema is more common in adults and older children. The correlation appears to depend on the dose and prolonged exposure to cigarette smoke, increasing the risk of developing eczema over time.

How does tobacco act to induce its effects on eczema?

Although the direct effect of tobacco on the skin is not clearly established, tobacco smoke is believed to degrade the skin barrier function through the effects of free radicals, thereby facilitating the penetration of allergens into the body and causing eczema. Researchers also believe that the chemical substances contained in cigarettes (formaldehyde, lead, tar, nicotine, etc.) disrupt the microcirculation of blood, thus compromising the oxygenation of the skin, and delay wound healing because they inhibit the migration of fibroblasts into the damaged skin.

We also know that tobacco smoke triggers aberrant immune responses, by increasing the levels of eosinophils (a type of white blood cell involved in allergy phenomena) and the production of pro-inflammatory agents ( TNF-𝛼, IL-6, etc.), which would directly impact the skin's protective barrier. This phenomenon would then increase the risk of atopic dermatitis or promote the occurrence of eczema flare-ups.

For instance, benzopyrene, one of themain compounds found in tobacco smoke, is capable of regulating inflammation. A study conducted in 2016 revealed that mice exposed to benzopyrene exhibited higher levels of an immune receptor (AhR) in the epidermis, leading to an increase in the migration of immune cells (Langerhans cells), as well as levels of pro-inflammatory cytokines (IL-5, IL-13 and IL-17).

It should be noted that smoking does not invariably cause eczema in smokers. Some individuals are predisposed to develop a skin reaction in response to tobacco due to genetic factors or individual sensitivities. Furthermore, as eczema is a complex disease, it is likely that multiple factors interact to influence its onset and progression.