Thanks for all the replies, you’ve pretty much confirmed what I thought.
When I went to work today, I also had quite a few people recommend vinegar (after they had finished laughing and pointing out that I looked like a raccoon). I tried a bit of white vinegar, and it took the sting away almost immediately. Of course, the down-side to this was that I smelled like a gym sock all night long…
From past experience, I too can recommend vinegar for treating sunburn. It does take the sting away quickly, for at least a few hours. Then reapply. But the smell is a disadvantage – you seem like a pickel for a while – but when it stops the hurt, who cares?
Vinegar is a mild acid, rather like the tannic acid of steeped tea that koeeoaddi suggested. And I think that aloe vera is mildly acidic, too. Maybe this is a common link?
But TheLoadedDog’s bicarbonate of soda bath would be mildly basic, not acidic.