AbstractBlue light is a UV‐free irradiation suitable for treating chronic skin inflammation, for example, atopic dermatitis, psoriasis, and hand‐ and foot eczema. However, a better understanding of the mode of action is still missing. For this reason, we investigated whether dendritic cells (DC) are directly affected by blue light irradiation in vitro. Here, we report that irradiation neither induced apoptosis nor maturation of monocyte‐derived and myeloid DC. However, subsequent DC maturation upon LPS/IFNγ stimulation was impaired in a dose‐dependent manner as assessed by maturation markers and cytokine release. Moreover, the potential of this DC to induce cytokine secretion from allogeneic CD4 T cells was reduced. In conclusion, unlike UV irradiation, blue light irradiation at high and low doses only resulted in impaired DC maturation upon activation and a reduced subsequent stimulatory capacity in allogeneic MLRs with strongest effects at higher doses.