Yes, that is my foot.
A quick (because it *is* Wednesday morning) explanatory post about blisters then... From what I can gather, it's a bit like when the cashier at the supermarket till hands you a plastic bag - we all take our own re-usable bags these days, of course, but bear with me - and you have to stand there for five minutes, trying to prise it open. Lemons are rolling at you, tins of tomatoes and boxes of tea are stacking up... and you still can't get the damn thing to open up. Anyway, as we all know, the way to do it is to rub the plastic between your fingers until the two layers separate. Theeeeere we go.
Like the plastic bag, skin has different layers. And as with the plastic bag, it just takes a little bit of friction (rubbing) to open up a space between the layers. This is what happens when you run a long way - possibly wearing ill-fitting shoes - and the friction causes the connections between the surface and the underlying layers to break. In the case of your skin, the space that's created starts to fill with liquid - serum, which is blood devoid of the red blood cells. Boom. You have a blister.
I like Jae Won Joh's pictorial explanation of this process on Quora.
What are we told to do about blisters? 1) Stop the friction (get better fitting shoes) 2) Stop the running (blisters will go away on their own) 3) DON'T BURST THE BLISTER (in case evil bacteria get in)! Don't be mad medical peoples, but I have to confess that if I have a heavy training schedule and can't wait for a blister to go down, I will sterilise a needle and make a tiny hole to release the fluid... Then stick some antiseptic cream and a plaster on it. Am I really naughty?