I had two mosquito bites that swelled to little eggs on my arm. I mixed a little charcoal with water and dabbed that on. The itch stopped immediately and I kept putting it on several times. The swelling went down as well.
My husband cut some tree branches and got three spider bites on the back of his knee. Two of them had already started seeping by the time he showed it to me and one especially looked pretty scary. We put some charcoal on mixed with water and then covered everything with bandaids. We changed this several times and after about three days one bite is gone and the other two look like they are healing nicely.