Emollients and atopic dermatitis: proven benefits

Emollients (substances that promote relaxation and softening of the skin) are already one of the essential treatments for atopic dermatitis. Employed to restore the cutaneous barrier of the skin, they are also used as a preventive measure in infants at risk. It is not known precisely how they act on the cutaneous microbiota and it needs to be clarified to improve the therapeutic solutions.

Atopic dermatitis is a chronic, allergic, inflammatory skin disease which manifests mainly during the first six months of life³². Not all newborns are equally susceptible: babies whose parents themselves suffer from atopic dermatitis or an allergic disease such as asthma or allergic rhinitis have in fact a two–even three–times greater risk Emollients and atopic dermatitis: proven benefits of developing the disease than babies with no family history³³.

Staphylococcus aureus: an identified enemy

The skin is permanently colonized by the microorganisms which form the cutaneous microbiota. But in atopic dermatitis, its barrier function is impaired and no longer provides the same level of protection against external attacks. This condition weakens the skin, makes it more vulnerable and subject to colonization by undesirable microbes³⁴. In this case, Staphylococcus aureus plays a crucial role: analyses have shown that, on the skin of infants suffering from atopic dermatitis with lesions, the bacterium was present in more than 90% of cases This figure falls to 78% for dermatitis without lesions, but drops to 10% if the skin is healthy³⁵. The density of Staphylococcus aureus is therefore thought to be correlated with disease severity. Since this is not however systematic, the researchers consider that the disease displays heterogeneity between individuals. Other methods of analysis have enabled better characterization of the bacterial communities of skin affected by this disease: of course the proportion of Staphylococcus aureus increases during the flare phases, but significant changes have been observed in other bacteria (classic or more rare) during and after treatment³⁶.

The role of emollients better understood

Effective and widely approved in the treatment of atopic dermatitis in infants, emollient creams rehydrate and repair the damaged skin by regenerating injured tissue, and reduce disease severity³⁷. Their regular application over the first six months of life to the skin of babies with a high probability of developing the disease might prevent its manifestations, although results diverge from one individual to the next³⁸. Some researchers have studied these emollients, in order to better understand their preventive action on the cutaneous flora. They compared different skin parameters, monitored the development of atopic dermatitis and genetically analyzed skin samples taken from different places on the body, depending on whether the infants (all at risk) had received emollient treatment or not³⁹.

Result: the skin of infants treated beforehand had a lower pH than that of the control group (healthy skin has a slightly acidic pH, which helps it to function correctly, while that of skin with atopic dermatitis is higher⁴⁰, favouring colonization by Staphylococcus aureus). Modulation of pH might then be a means of rebalancing the cutaneous microbiota. Generally, the Streptococcus genus also clearly contributed to the differences observed in the samples from the two groups. The skin of the infants who received treatment contained a richer and more diverse bacterial population, which resembled a restoration of the balance of the cutaneous microbiota. In particular, Streptococcus salivarius bacteria were present in greater numbers. The latter colonize the organism (especially the mouth) from the first moments of life and seem to have a protective role: they are present in higher levels in infants who do not have atopic dermatitis than in those who have the condition. This result is consistent with those of other studies conducted in older children which showed that the higher the proportion of Streptococcus salivarius, the milder the atopic dermatitis.

These data confirm the benefits of the long-term use of emollients as a preventive measure in infants at high risk. They provide new information on the way in which emollients act, although the mechanisms involved and the impact of localized changes in the cutaneous microbiota on the development of the disease in these infants remain to be identified.