Most pour-on tick and flea products are alcohol based. This alcohol mixes with the sebum of the skin and hair and disperses over the body. When the alcohol evaporates, it leaves medication around the body. The manufacturers recommend not using the product 2 days before or 2 days after bathing. What do you think the efficiency would be if you stripped all the sebum off with a harsh shampoo or bathed without a good conditioner?