Re: Why does skin itch after it comes into contact with grass?

Well, you almost guessed right. It is our skin's sensory function, that is 
responsible. Now, one of the major functions of the skin is to protect the 
body from anything outside that might harm it. So, the skin senses the 
grass as something which might cause it harm. There are small receptors on 
the skin which pick up these sensations and accordingly try to get away 
from the harming thing. So, it makes you itch, which persuades you to get 
up and thus, unconsciously, you comply to the body's  senses by getting 
away from the grass. 
But, the thing is, this response is highly variable in people. Some people 
might not feel the itch at all. This is all an individualistic response of 
the body. Something like you get more sick than others for a particular 
disease, or you have to take medicine for a longer time to cure yourself 
than someone else, who might get cured just as easily.