This cannot be used as a rashguard due to its length. A rash guard is worn by surfers under wetsuits, and prevents the wetsuit from chafing the skin. One could wear this under a wetsuit if he did not mind the extra material at the waist. However, I believe most people are buying this to prevent sunburn, not rashes. I cannot recommend this item be worn in the water due to the fact that it is very long and expands when wet. This means the rashguard would be hanging on the wearer. I do like the item, but would never wear it swimmimg. The bulk could become a safety hazard. This runs small. I have been wearing rash guards for years and know how they are meant to fit. I am a size 8 and a medium in clothing, 57 and 145 pounds. Based on the reviews, I ordered up from my normal size. I ordered an XL, knowing I would not swim in such a long top. I bought it to wear as a cover up.  I thought it would fit a bit loosely and it does not. I wanted a loose fit so I could have some breathimg room- rash guards are made to fit snugly. I wear rash guards often while sitting in my beach chair because I get sick after being in the sun, but wanted something looser that would not cause my bathing suits to bunch up. I also did not want a very tight fit when wearimg this as a cover up. While it is not skin tight, the item is not as loose as I had hoped. Keep in mind I ordered two sizes up from my normal size. I do like the fact that this may be worn as a shirt or cover-up, and the yellow is a pretty shade. Someone of my size, who usually wears ONeill rash guards, should not have to order three sizes up to get a loose fit. I also wear Roxy, and the sizes are consistent. Therefore, I suggest ordering at least two sizes up for the fit of a regular shirt, one size up for a typical rash guard fit, and three sizes up for a loose fit. Also, unless tou are very short, this will not work as a dress cover up. It is not long enough. I have ro constantly pull it down.