We all know that one should apply sunblock first (say 15 minutes before actual exposure to the sun in order to give our skin time to absorb the stuff) — and then apply insect repellent (DEET) afterwards so it stays on the surface to do its job.
But I prefer to apply lotion just once rather than lathering layer by layer. Last week, on a 2-day hike up Mt. Whitney, I pre-mixed a 50/50 batch of REI 45 SPF sunblock and 3M Ultrathon 30% DEET. While both products boast "all day protection" — my experience using them separately is that I need to reapply both of them again in the afternoons when doing long day hikes.
Bottom line test: Lathering the pre-mixing lotion and therefore applying just HALF the recommended quantity of each — will the mixture still provide good protection and will it require only one re-application during the course of a long day? In other words, will the mixture work just as well as compared to applying both in separate layers?
Findings:
1. Sun protection — YES! At 10-14k altitude — not wearing hat or bandana — and with the sun beating down for 12 hours each day — a morning application plus a second one in mid-afternoon gave me the protection I needed. No perceptible difference as compared to the past times when I applied the two products separately.
2. Bug Protection — Unfortunately (for testing purpose) — insects were few and far between up in Whitney. The few insects there were (a handful of flies and whatnots) did not land on me.
Conclusion: I am happy with the mixture's sun block performance and will test its bug repellent property again in a future trip. If the latter passes, then pre-mixing will save pack space, weight, and time.
