How is it that a breathalyzer can measure 
the alcohol content in someone’s blood,

hours after they had their last drink, 
based on their breath alone?

Exhaled breath contains trace amounts 
of hundreds, even thousands,

of volatile organic compounds:

small molecules lightweight enough 
to travel easily as gases.

One of these is ethanol, 
which we consume in alcoholic drinks.

It travels through the bloodstream 
to tiny air sacs in the lungs,

passing into exhaled air 
at a concentration 2,000 times lower,

on average, than in the blood.

When someone breathes 
into a breathalyzer,

the ethanol in their breath 
passes into a reaction chamber.

There, it’s converted to another molecule,
called acetic acid,

in a special type of reactor that produces
an electric current during the reaction.

The strength of the current 
indicates the amount of ethanol

in the sample of air, 
and by extension in the blood.

In addition to the volatile 
organic compounds like ethanol

we consume in food and drink,

the biochemical processes of our cells 
produce many others.

And when something disrupts 
those processes, like a disease,

the collection of volatile 
organic compounds in the breath

may change, too.

So could we detect disease 
by analyzing a person’s breath,

without using more invasive 
diagnostic tools

like biopsies, blood draws, and radiation?

In theory, yes,

but testing for disease is a lot more 
complicated than testing for alcohol.

To identify diseases,

researchers need to look at a set 
of tens of compounds in the breath.

A given disease may cause 
some of these compounds

to increase or decrease in concentration, 
while others may not change—

the profile is likely to be different 
for every disease,

and could even vary for different stages 
of the same disease.

For example, cancers are among 
the most researched candidates

for diagnosis through breath analysis.

One of the biochemical changes 
many tumors cause

is a large increase 
in an energy-generating process

called glycolysis.

Known as the Warburg Effect,

this increase in glycolysis results 
in an increase of metabolites like lactate

which in turn can affect a whole cascade 
of metabolic processes

and ultimately result 
in altered breath composition,

possibly including an increased 
concentration of volatile compounds

such as dimethyl sulfide.

But the Warburg Effect is just one 
potential indicator of cancerous activity,

and doesn’t reveal anything 
about the particular type of cancer.

Many more indicators are needed 
to make a diagnosis.

To find these subtle differences,

researchers compare the breath 
of healthy people

with the breath of people 
who suffer from a particular disease

using profiles based on hundreds 
of breath samples.

This complex analysis 
requires a fundamentally different,

more versatile type of sensor 
from the alcohol breathalyzer.

There are a few being developed.

Some discriminate 
between individual compounds

by observing how the compounds move 
through a set of electric fields.

Others use an array of resistors 
made of different materials

that each change their resistance 
when exposed to a certain mix

of volatile organic compounds.

There are other challenges too.

These substances are present 
at incredibly low concentrations—

typically just parts per billion,

much lower than ethanol concentrations 
in the breath.

Compounds’ levels may be affected 
by factors other than disease,

including age, gender, nutrition, 
and lifestyle.

Finally, there’s the issue

of distinguishing which compounds 
in the sample

were produced in the patient’s body

and which were inhaled 
from the environment

shortly before the test.

Because of these challenges, 
breath analysis isn’t quite ready yet.

But preliminary clinical trials 
on lung, colon,

and other cancers 
have had encouraging results.

One day, catching cancer early 
might be as easy as breathing in and out.