Why does scratching an itch cause it to spread?

[aychamo]

Hey guys;

I got into red bugs a while back, and everyone was warning me "Don't scratch! They will spread!" Well, I recovered from that, but I got into something else now and I'm itching again.

Anyway, I'm wondering if there is an validity in the "dont scratch your itch because they will spread" statement?

I know the good thing of scratching is that momentary relief of the irritating itch. But I know that also with scratching you risk secondary infection from bacteria by opening the wound futher.

Also, as far as answering my own question, my thought was that perhaps whatever is irritating your skin and causing the itch, when you scratch it, that you will futher irritate more skin (probably creating small tears in the epidermis), and when you scratch you will be moving some of the irritating agent (whatever is irritating the skin) and it will get into the small tears in the skin you just made, which then makes the body have more inflammation.

Does that sound kind of correct?

 

[Moonbear]

For things like bites, scratching will do as you suggested, irritate the surrounding skin by scratching off the skin of the surrounding area, not by actually transferring any of the irritant. Spreading the irritant would be the case for something like poison ivy, where the oily substance that leads to the rash can be spread by touching it. Avoiding scratching is more related to what you mentioned of opening up the skin to further infection.