The skin microbiome of atopic dermatitis patients and healthy volunteers will be studies by collecting and analysing skin swabs on different timepoint. Additional, effort will be made to isolate and characterize Lactobacillus spp. and other beneficial micro-organisms on the skin. Second aim of this study is to evaluate a topical probiotic cream in atopic dermatitis treatment. A double-blind placebo-controlled intervention study will be performed in parallel with the skin microbiome analysis. Both clinical effect on the symptoms of atopic dermatitis and effect on the skin microbiome and survival of beneficial bacteria on the skin will be evaluated.

Probiotics are live micro-organisms which when administered in adequate amounts can exert a health benefit on the host. This health-promoting effects have been extensively studied in the gastrointestinal niche but it becomes more and more clear that other niches are also interesting for the potential of probiotics. Recent breakthroughs in 'next generation sequencing' (NGS) technologies are making it now possible to map the microbiota after DNA extraction, which is very interesting for bacteria that are not or difficult to cultivate. The research into the microbiota of the skin with such new NGS technologies shows that there is also an equilibrium in the skin composition of the microbiota and that there is a disturbance of the skin microbiota in atopic dermatitis (AD). The etiology of AD is complex, with the manifestation of the disease being influenced by various genetic and immune mechanisms acting in concert with environmental factors. A reduction in the skin microbial diversity is often observed and flares are characterized by an abundance of skin pathobionts such as Staphylococcus aureus. Therefore, topical probiotic strains could have a positive effect on the skin microbiome and function by inhibiting pathogens, restoring the skin microbiome and/or barrier function and executing anti-inflammatory effects on the skin cells. The main objectives of this study are to analyse the skin microbiome in healthy volunteers and patients AD to obtain in depth data of the composition of the skin microbiome and identify possible biomarkers for AD. In parallel, a double-blind placebo-controlled study with topically applied live lactobacilli will be performed to give more insights in the working mechanisms of lactobacilli on AD skin. More specifically to evaluate the effect of the 'live' Lactobacillus species as 'active ingredient' in relation to acne symptoms and skin microbiome modulation.

Inclusion Criteria:

• Patients with atopic dermatitis and healthy volunteers

Exclusion Criteria AD patients:

• no use of topical antibiotics and/or corticosteroids within 2 weeks before the start
• no use of oral antibiotics within 1 month before the start
• no immunodeficiency disease

Exclusion Criteria Healthy Population:

• no use of topical antibiotics and/or corticosteroids within 2 weeks before the start
• no use of oral antibiotics within 1 month before the start
• no immunodeficiency disease
• no history of atopic dermatitis or other inflammatory skin disorders