There is a myth that sun will help improve acne.Sun exposure can worsen acne in people prone to acne.The temporary effects of a tan and the drier skin creates the illusion that the sun improves acne. However, UV rays damage the skin and make it dry but your skin rebounds by producing more oil to compensate which often makes acne noticeably worse. Plus alot of topical acne medications make skin more photo sensitive to the sun and cause it to burn more easily. Also exposure to excess sunlight causes hyperpigmentation which can make acne scars darker.
Look for a broad spectrum SPF formula that you like and make it a daily habit for healthy skin for a lifetime. Skinceutical Physical Matt UV Defence SPF 50.