Question: Can I sunbathe on Shabbos?
Answer: R’ Yitzchak Yaakov Weiss (Minchas Yitzchak 5:32:2) writes that whether one is sunbathing for medical reasons or just because they would like a tan, one mustn’t do so on Shabbos. Firstly, he writes, that according to the the Shulchan Aruch (OC 303:25), the melacha of tzoveia, dyeing, applies to colouring one’s body. Additionally, he argues, that when it is exceedingly hot, sunbathing can be a painful experience and so must be avoided on Shabbos (See Rambam, Shabbos 21:29). Lastly, sunbathing is normally preceded by rubbing sun-cream into oneself, and often ointments afterwards. As both of these are forbidden on Shabbos, this is another reason not to sunbathe on Shabbos (See Chelkas Yaakov 4:17:1).
R’ Binyamin Zilber (Az Nidberu 2:30) writes that while one can’t sunbathe for health reasons, one may do so on one’s own balcony for relaxation.
R’ Moshe Feinstein (Igros Moshe OC 3:45) writes that while photochromic lenses change colour in the sun, there is no issue of tzoveia as it is temporary and changes right back. R’ Yehoshua Neuwirth (Shemiras Shabbos Kehilchasa 18:n70) compares this to sunbathing, which leaves a temporary tan, implying that it isn’t a problem.R’ Pesach Eliyahu Falk (Machazeh Eliyahu 65:6:24) writes that while purposely sunbathing may be problematic, one can certainly relax outside in the sun if their intention isn’t to get a tan.