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

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

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Exhaled breath contains trace amounts 
of hundreds, even thousands,

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of volatile organic compounds:

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small molecules lightweight enough 
to travel easily as gases.

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

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

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

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on average, than in the blood.

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When someone breathes 
into a breathalyzer,

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the ethanol in their breath 
passes into a reaction chamber.

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

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

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The strength of the current 
indicates the amount of ethanol

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

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In addition to the volatile 
organic compounds like ethanol

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we consume in food and drink,

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the biochemical processes of our cells 
produce many others.

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And when something disrupts 
those processes, like a disease,

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the collection of volatile 
organic compounds in the breath

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may change, too.

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

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without using more invasive 
diagnostic tools

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like biopsies, blood draws, and radiation?

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In theory, yes,

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

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To identify diseases,

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

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A given disease may cause 
some of these compounds

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

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the profile is likely to be different 
for every disease,

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

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For example, cancers are among 
the most researched candidates

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for diagnosis through breath analysis.

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One of the biochemical changes 
many tumors cause

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is a large increase 
in an energy-generating process

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called glycolysis.

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Known as the Warburg Effect,

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

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which in turn can affect a whole cascade 
of metabolic processes

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and ultimately result 
in altered breath composition,

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possibly including an increased 
concentration of volatile compounds

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such as dimethyl sulfide.

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

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

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Many more indicators are needed 
to make a diagnosis.

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To find these subtle differences,

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researchers compare the breath 
of healthy people

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with the breath of people 
who suffer from a particular disease

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using profiles based on hundreds 
of breath samples.

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This complex analysis 
requires a fundamentally different,

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more versatile type of sensor 
from the alcohol breathalyzer.

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There are a few being developed.

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Some discriminate 
between individual compounds

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

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Others use an array of resistors 
made of different materials

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that each change their resistance 
when exposed to a certain mix

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of volatile organic compounds.

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There are other challenges too.

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These substances are present 
at incredibly low concentrations—

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typically just parts per billion,

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much lower than ethanol concentrations 
in the breath.

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

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including age, gender, nutrition, 
and lifestyle.

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Finally, there’s the issue

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of distinguishing which compounds 
in the sample

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were produced in the patient’s body

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and which were inhaled 
from the environment

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shortly before the test.

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

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But preliminary clinical trials 
on lung, colon,

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and other cancers 
have had encouraging results.

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