What Could Dark Brownish Lines/scars On Wrist Suggest?

My wife has brownish long lines on one of the insides of her wrist. Should she seek medical advise. It is only on one wrist. She is 45 and we were just in Mexico in the sun for a few weeks. It lloks like a scar that is tan but she has no scar there. No pain or itch as well. It is fading now we are back.