I know some women on here rub it in, but the instructions do not say to rub in the gel - but to apply it. I interpret that is spreading it and leaving it to dry. If it meant to rub it in it would say so! I don't use oestrogen gel but I use testosterone gel and this is applied in the same way. The idea is that it is absorbed before it dries, so if rubbing it in causes it to dry or the solvent to evaporate more quickly I would suggest that less is absorbed using this method (rubbing in).
I would also not apply it to your upper body at all. Interestingly oestrogel differs from Sandrena gel in location of gel application. Sandrena only says the skin of the lower trunk of the right or left thigh, but Estrogel says "clean, dry, intact areas of skin e.g. on the arms and shoulders, or inner thighs." I would suggest there is a concentration gradient from the site of application leading away from it and therefore a possibility that if applied to the upper arms or shoulders a higher concentration of oestrogen may reach the breasts. However I have not searched for any research on this and I would be surprised that upper body application would be suggested if it were harmful. In that case though - why doesn't Sandrena also suggest upper body application is OK?
Hurdity x