Google has released "category blocking" feature to all AdSense publishers in English-speaking countries.
"General category blocking is an important update to new AdSense interface that offers more controls over the ads appearing on your website. It helps you scalably prevent competitors' ads and ads that you mightn't find suitable for your audience from appearing on your site. With this new control, you can opt out of receiving ads from across 170 specific categories, including finance, travel, job, and automotive" explains Google.
"We show the percentage of total revenue and total impressions for each category to give you insight into categories of ads that appear on your site and the relative spend in those categories. Keep in mind that blocking categories may have a negative impact on your potential revenue so it's important to review the % of total revenue and total impressions carefully before deciding to block a certain category," Google said.