Interesting thought Minusminnie! Just checked the instructions for various HRT products I've got/used & instructions differ . . .
Lenzetto not above 25 but says don't refrigerate

FemSeven Conti says not above 30
Estradot temp not specified but says don't refrigerate
Testogel no special storage conditions
Estriol 0.01% (instructions same as for stronger Ovestin) not above 25
Vagifem says do not refrigerate
Have moved my Estriol to the fridge, but if it matters suspect too late as has been 30ish here for days & feels almost as hot indoors as out & is hotter at night

As Lyncola says these products are used in climates hotter than we get in the UK, but it is a bit of a concern given how much we rely on them working as they should & a pack/tube etc may last a long time.