BackgroundPolar microalgae contain unique compounds that enable them to adapt to extreme environments. As the skin barrier is our first line of defense against external threats, polar microalgae extracts may possess restorative properties for damaged skin, but the potential of microalgae extracts as skin protective agents remains unknown.PurposeThis study aimed to analyze compound profiles from polar microalgae extracts, evaluate their potential as skin epithelial protective agents, and examine the underlying mechanisms.MethodsSix different polar microalgae,Micractinium sp. (KSF0015 and KSF0041),Chlamydomonas sp. (KNM0029C, KSF0037, and KSF0134), andChlorococcum sp.(KSF0003), were collected from the Antarctic or Arctic regions. Compound profiles of polar and non-polar microalgae extracts were analyzed using gas chromatography-mass spectrometry (GC-MS). The protective activities of polar microalgae extracts on human keratinocyte cell lines against oxidative stress, radiation, and psoriatic cytokine exposure were assessed. The potential anti-inflammatory mechanisms mediated by KSF0041, a polar microalga with protective properties against oxidative stress, ultraviolet (UV) B, and an inflammatory cytokine cocktail, were investigated using RNA-sequencing analysis. To evaluate the therapeutic activity of KSF0041, an imiquimod-induced murine model of psoriatic dermatitis was used.ResultsPolar microalgae contain components comparable to those of their non-polar counterparts, but also showed distinct differences, particularly in fatty acid composition. Polar microalgae extracts had a greater ability to scavenge free radicals than did non-polar microalgae and enhanced the viability of HaCaT cells, a human keratinocyte cell line, following exposure to UVB radiation or psoriatic cytokines. These extracts also reduced barrier integrity damage and decreased mRNA levels of inflammatory cytokines in psoriatic HaCaT cells. Treatment with KSF0041 extract altered the transcriptome of psoriatic HaCaT cells toward a more normal state. Furthermore, KSF0041 extract had a therapeutic effect in a mouse model of psoriasis.ConclusionsBioactive compounds from polar microalgae extracts could provide novel therapeutics for damaged and/or inflamed skin.Supplementary InformationThe online version contains supplementary material available at 10.1186/s40659-023-00454-1.