I'm not a huge believer in stress = acne. Can it make the already in place acne seem worse, of course, it's called stress.
Make a list of what exactly was different. You arleady said sun, and I imagine you were in the water a lot, so salt water as well. Next you'll want to look at the differences between being at home and being on that vacation. Being at home you use regular water to shower (this actually dries the skin), no more salt water and not as much sun. The sun can cause your skin to peel, a natural peeler that can lift the dead skin. The sun will also give you a reddish hue to mask any of the so called marks for awhile. Next the salt water will go in and clean the pores, this will burn if your pores are open. If you add all these things in you will have a face that appears to be acne free. Then you get home and about 1-2 weeks later your skin isn't looking so great. The red sun hue is fading and your natural color is returning, along with the red marks. The salt water is a great thing for clogged dirty pores, however, it can be drying on the skin. I believe a combination of these things led to the appearance of clear skin.
Best way to beat acne (IMO) is to allow your skin to heal itself, do not dry it out. No washing, scrubbing, no WATER (as water dries the skin), clean with a dry towel gently daily on the surface of dry skin.
Edited by geoguy1, 10 July 2014 - 02:23 PM.