I am an admitted coffee addict, and I work in an office. That means that - as I write this - a downright filthy mug is sitting on my desk, with the last dregs of my morning cup dried on the bottom.

Grossed out? You shouldn't be.

That's not just my opinion. Experts actually say that a dirty coffee mug isn't as disgusting as it seems.

And you shouldn't feel pressure to clean it, unless the sight of your mug makes your coworkers sick.

How often should I wash my coffee mug?

Infectious disease expert Jeffery Starke kicked off the biggest office debate of all time in an interview with The Wall Street Journal.

The professor from the Baylor College of Medicine says people spend way too much time fretting about their dirty mugs.

"Of all the things people have to worry about, getting sick from an old coffee mug is at the bottom," he insists.

Starke says that as long as you follow a few simple rules, there's no need to clean your mug:

• Don't share your mug, because obviously this would spread germs from one person to another.
• Don't add milk or cream. Unlike coffee dregs, these liquids promote mold growth. Clean your mug thoroughly if you use them.

Does that mean a dirty mug is actually germ-free? Absolutely not.

"But remember the vast majority came from the person who used the cup," Starke said. Even if you were sick, it's unlikely you would catch the illness again from your old germs.

"During cold and flu season, I would guard my mug and make sure no one else is using it," Starke warns. "Don't share."

It may sound like a nasty habit, but Navy veterans actually make a proud tradition out of keeping a dirty mug.

The stains on a sailor's mug are seen as a sign of long service, and some veteran crewmembers even insist it adds flavor to the brew.

"You may not be able to embrace your loved ones while you are gone, but at least you can still taste the same coffee you drank the day you left," as one blogger put it.

Can a dirty coffee mug make me sick?

If your coworkers give you grief about your messy mug, tell them their clean one is probably crawling with germs.

It turns out the average office sponge is nastier than a used mug - but that doesn't mean your mug is perfectly clean.

"All sorts of germs and bacteria can live on and in your cup, especially if you are in a shared space," Melissa Maker, who hosts the YouTube show Clean My Space, told How Stuff Works.

The warm, damp environment of a mug is just too inviting for germs like the cold virus or strep throat to pass up.

In a particularly gross study of office coffee mugs from 1997, 41% of them tested positive for coliform bacteria (from fecal matter).

Starke would argue that if you're sitting close enough to a sick person to catch their germs, that's a bigger worry than your dirty mug.

As he told the Journal, "most viruses don't live long outside the body."

How to clean a dirty coffee mug

If you're anxious about germs, it wouldn't hurt to give your mug a cleaning with soap and warm water each night.

But use paper towel or your own hands, not a sponge that is crawling with your coworkers' bacteria.

"The sponge in the break room probably has the highest bacteria count of anything in the office," Starke reminds us.

Stains should wipe off easily, but if you've ignored them too long your mug might still have a darker shade on the inside.

A blast from a tough, all-purpose cleaner like 409 make stains wipe off easily. (We may make a small commission from this Amazon affiliate link, but this is a great product.) Just rinse the mug off thoroughly afterwards.

If you prefer natural cleaning solutions, pantry staples like baking soda, vinegar, lemons, and salt will all do the trick.

Do you wash your coffee mug, or let the stains linger?

[H/T: Today, HowStuffWorks, Wall Street Journal]