What's this rash?

[Illbefinejustbloodyfine]

First noticed it a week ago, after a really long walk. I thought my arm had rubbed a bit. Today though it is significantly worse, a bit itchy but very red and raised, larger is size but much denser if that makes sense.

I also, today, have a few spots on my inner upper arm, as if its spreading a bit.

Photo

That looks like prickly heat perhaps - were you warm on the walk?

@qwertyqwertyqwertyqwerty yes! It was very warm at times, I used sun cream (which my face reacted to with spots)

Allergic eczema. That area and the backs of the knees are typical if you've had a lot of foods like tomatoes, strawberries, eggs and citrus fruits recently, it's usually one of them that causes it.