Thick skinned?

[sjmaderious]

Hi All,
This is my first post, but I love the site! I was just wondering if anyone could tell me why my tomatoes seem to have such thick skins? I grow several types in my yard and water them regularly. In the past seasons I never noticed this, but this year all the tomatoes seem to be very thick skinned, so that when I eat a cherry tomato, I'm left chewing a wad of skin after everything else is gone. Any hints? Thanks! -Steve