*2.4. Cell Viability Assay*

HaCaT cells (5 ×10<sup>4</sup> cells/well) were seeded in a 24-well plate containing DMEM and supplemented with 10% FBS and varying concentrations of Ectoine (0.5–1.5 μM, 24 h). Then it was irradiated in the absence or presence of UVA (3 J/cm2). B16F10 cells (5 × 10<sup>4</sup> cells/well) were seeded in a 24-well plate containing DMEM and supplemented with 10% FBS and varying concentrations of Ectoine (100–400 μM, 72 h). The cells were washed with PBS and an MTT cell viability assay was conducted [21].
