A scientist’s take: why is the US swimmers’ face turning purple? Evidence of doping? ITPP? EPO?

During Pairs Olympics, some US swimmers’ facial color got a lot of attention. Why do they look so red, even purple in some photos? Some famous internet experts started endless speculation or in this case, serious doping accusations. Canadian fitness coach Greg even put out a specific drug, ITPP.
So, are those doping speculation legit? What is ITPP? can it really change face color? Can US athletes really evade anti-doping test?
Let’s do some fact based analysis

00:00 Purple face?
02:18 what is ITPP?
14:19 why ITPP will not work as some people suggested
23:35 ITPP can be detected
26:48 Biological passport
38:25 My thoughts on purple face