I can’t answer the first question. Impetigo is caused by Staphylococcus aureus and Streptococcus pyogenes. These two bacteria are on our skin at all times and both are opportunistic so it has nothing to do with your hygiene.

As to the second question, ecthyma, one of the three types of impetigo, is known for scarring the skin. I know of no "home remedies" for treating scars but there are products you can buy at a pharmacy or market. Try Mederma topical gel made by Merz Pharmaceuticals. Here’s their link (you can buy online, too):

http://www.merzusa.com/mederma.html