Many SEO ‘gurus’ recommend dividing your URL up into separate keywords by using underscores. So for example, if you were selling men’s designer clothing you might have a URL like this:
However, this is wrong. And it’s wrong for two very good reasons. First of all, let’s consider the purely practical reason. Let’s say that someone has found a link to your website and is reading the URL out to a friend. Your URL will look like this when it’s displayed online with a line underneath it:
Can you see the potential problem? The underscores are there, but they’re completely invisible, which means that anyone reading out or copying that URL will try to put spaces in between the three words. This of course will mean that these URL’s won’t get you to the page, and on top of this a 404 error will be generated, and this could potentially harm your search engine ranking.
But there’s a second reason why using underscores is bad. Google has made it clear in the past that when they see a URL which includes underscores they strip these out. This means that rather than your URL being optimised for the keyphrase “men’s designer clothing” it is actually listed as being optimised for the keyword “mensdesignerclothing”, which is hardly good SEO.
Instead of using underscores then you should use hyphens or dashes, because when Google sees a URL which includes dashes it treats the words as distinct. So if your URL looks like this:
Google will now see the three words as distinct, and a single optimised phrase, “men’s designer clothing”. If you already have URLs formatted with underscores, and you’ve already carried out a great deal of marketing to optimise and promote these pages then it’s probably not best you change the URLs now as you’ll only end up losing page authority generating 404s or having to create a whole heap of 301 redirects. But for any new pages you create, or if you’re starting fresh with a new website make sure that you use hyphens or dashes rather than underscores, for both of these very good reasons.