Is tanning scriptural? Would it be a sin for one to tan?
Tanning serves no purpose beyond cosmetic purposes. Our society currently sees tans as an indication of healthy outdoor living and also a sign of wealth since few people have the idle time to get tanned over a large area of their body. In the past was the opposite. Being tanned meant you were more likely a common laborer who worked out doors. It was the rich who could afford to stay out of the sun. "I am dark, but lovely, O daughters of Jerusalem, like the tents of Kedar, like the curtains of Solomon. Do not look upon me, because I am dark, because the sun has tanned me. My mother's sons were angry with me; they made me the keeper of the vineyards, but my own vineyard I have not kept" (Song of Solomon 1:5-6).
You have to realize that looks are temporary things. "Charm is deceitful and beauty is passing, but a woman who fears the LORD, she shall be praised" (Proverbs 31:30). We admire tans now, but later in life the same people tend to have more wrinkled skin. Things in this life are not nearly as important as our spiritual life. "Do not let your adornment be merely outward -- arranging the hair, wearing gold, or putting on fine apparel -- rather let it be the hidden person of the heart, with the incorruptible beauty of a gentle and quiet spirit, which is very precious in the sight of God" (I Peter 1:3-4). We have to keep proper priorities.
Another potential problem with tanning is that some wear very little clothing while tanning, which would be immodest if others saw you.