Always before putting on wetsuit. 1 - putting it on after the swim would involve towelling off as sunscreen won't stick to wet skin. 2 - don't want to waste time in transition.

I always do before putting on the wetsuit, but TBH, it never lasts long enough and I'm always super burned by mid-run. I always forget to keep more in T2 but that's what I plan to do for my the next 70.3 (a small bottle that I can grab and then apply while I start running). I also want to switch from sleeveless to a long-sleeved racing suit but haven't looked much into that yet.

I'm blonde, with really fair skin that burns easily and badly.

Sunscreen coat 1 goes on first thing in the morning SPF 60+

I then wipe a little dollop on the top tube of my bike, apply to back of neck when I'm dry after the first few kms of the bike.

And a third dollop on the back of my race number bib which I wipe onto my arm and then rub on when I settle into my run pace.

Apply to dry skin right after you shower in the morning (or when you get up if you don't shower race morning). Reapply when you setup your transition area.
For 70.3 races I have some spray sunscreen designed for wet skin I can spray on in t2 on the way out as a refresh.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)