ELi5 Why do we brush our teeth first thing in the morning when we just brushed our teeth before bed?


I understand we have bad breath when we first wake up, but specifically why do our teeth need a second brushing first thing in the morning?

In: Biology

Have you ever smelled breath in the morning?

Because you’re essentially fasted and dehydrated for 6, 7, 8 hours at a time. You aren’t drinking fluids to flush the bacteria in your mouth. The same thing happens with people who don’t drink enough water throughout the day and go long periods without consuming food.

While you sleep, plaque-causing bacteria in your mouth multiply. That’s part of why you may wake up with a weird taste in your mouth and morning breath. Washing those bacteria right out with a fluoride toothpaste rids your teeth of plaque and bacteria.

Look, if you really hate it (like I do) then you don’t “have” to. But, the bacteria in your mouth multiply overnight, and then they can feed on the sugars from your breakfast, release acids, and damage your teeth. Also, if you miss one of your nighttime brushes and you’re only brushing once a day, then they have time to build a biofilm (think bacteria concrete) that your toothbrush can struggle to remove.

The people that say you should do it 30 minutes after breakfast are technically correct, but honestly, if you remember better first thing in the morning, do it then.

You don’t want to be on prescription toothpaste/mouthwash that has to stay on your teeth (ie no eating or drinking or rinsing) for 30 minutes after you brush because you’ve had 25 cavities in 5 years.

Why animals don’t have this problem?