I've heard of issues with them fogging up if your dog gets wet or if there's much moisture in the air. There's no real "seal" to keep things dry in there. No hands on experience of my own though. Typically if I haven't ran my dog in the high wheat/canola beans much in the summer during our first outing he'll get a little rough around the eyes. I just use a pad balm on them and no issues for the rest of the season.