It's a belief almost as old as the product

it's about.

Back in Egypt in the 12th century, a royal physician

warned that dairy can make you stuffy

in the head.

No one seems to know where he got that idea from,

but it's become a common belief worldwide

that gulping down a glass of milk or a grilled cheese

will leave you with more mucus than

a tissue can hold.

But... there seems to be no scientific evidence to back up that claim.

The idea that milk worsens congestion is one

of the most prevalent and persistent medical beliefs.

And while it might seem like a silly thing

to worry about, if dairy does increase mucus

secretion in the respiratory tract,

it would not only make colds more annoying—

it could be harmful to people with respiratory conditions

like asthma.

So far, only a few rigorous experimental scientific

studies have tried to determine if the milk-mucus

effect is real, and none have found support for the idea.

Several studies of asthmatics found that lung functioning—

like how much air you can blow

out in one second—

weren't affected by eating dairy.

And, in a study from the early '90s,

people who were infected with a common cold virus

didn't cough, sneeze or make any more nose gunk

if they drank milk.

That doesn't stop people from feeling like

they're more phlegmy after a tall glass

of 2%, though.

In a double-blind study published in the journal

Appetite in 1993, 169 participants said drinking

a flavored milk drink left a coating in their mouths,

and that after drinking it, they needed

to swallow more and their saliva was thicker.

The thing is, they said the same thing about

a soy placebo drink which did not contain

dairy.

And neither beverage significantly increased

the severity of mucus-related symptoms like

coughing or sneezing.

That could suggest the nocebo effect is at

play—the phenomenon where expecting something

bad to happen literally makes it happen.

Basically, the awful flipside of the placebo effect.

Or, it could be the fat in milk-like drinks

makes people's mouths feel a particular

way without actually changing mucus production.

You see milk is an emulsion—

droplets of fat hanging in water—

and saliva makes these

fatty drops clump together.

Globbier fat drops might feel a bit like mucus

or hang around in your mouth for longer,

making you think there's more mucus when there really isn't.

Though more research could really nail the coffin

shut on this idea, there's just no

evidence that dairy products actually cause

you to produce more mucus.

So go ahead!

Drink that milky boba tea, snack on that cheese stick,

whatever you wanna do, unless you've got

lactose intolerance or you're vegan or you

just hate cheese...I'm not in charge of your life.

Thanks for watching this episode of SciShow!

If you like learning about milk

and how it affects your body,

we've got more stuff for

you like our episode which explains

how people can drink milk as adults—

something most animals do not do.

{ ♪OUTRO }