I was prescribed loratadine for irritant dermatitis on chest.are those pills safe-how often side effects appear from them?is benadryl (diphenhydramine) better?

Gen'ly safe : Loratidine is a commonly used, generally safe medicine to use. It may make you sleepy, but usually LESS so then Benedryl. Everyone is different so you may not follow that rule of thumb. If you do become sleepy, be careful not to drive, or put yourself in a dangerous situation if that's the case.

Safe but useless: A topical Hydrocortisone cream and moisturizer would likely work better. Loratadine or any other antihistamine has no effect on irritant dermatitis or contact dermatitis. Even more important, avoid the irritant.