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Steroids: they’re infamous 
for their use in sports.

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But they’re also found in inhalers, 
creams to treat poison ivy and eczema,

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and shots to ease inflammation.

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The steroids in these medicines aren’t 
the same as the ones used to build muscle.

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In fact, they’re all based on 
yet another steroid—

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one our body produces naturally, 
and we can’t live without.

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Taking a step back, the reason 
there are so many different steroids

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is because the term refers to substances 
with a shared molecular structure,

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rather than shared effects on the body.

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Steroids can be naturally occurring 
or synthetic,

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but what all steroids have in common 
is a molecular structure

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that consists of a base of four rings 
made of 17 carbon atoms

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arranged in three hexagons 
and one pentagon.

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A molecule must contain 
this exact arrangement to be a steroid,

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though most also have side chains—

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additional atoms that can dramatically 
impact the molecule’s function.

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Steroids get their name 
from the fatty molecule cholesterol.

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In fact, our bodies make steroids 
out of cholesterol.

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That fatty cholesterol base 
means that steroids

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are able to cross fatty cell membranes 
and enter cells.

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Within the cell, they can directly 
influence gene expression

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and protein synthesis.

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This is different from many other types 
of signaling molecules,

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which can’t cross the cell membrane

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and have to create their effects 
from outside the cell,

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through more complicated pathways.

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So steroids can create their effects 
faster than those other molecules.

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Back to the steroids 
in anti-inflammatory medications:

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all of these are based on a naturally 
occurring steroid called cortisol.

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Cortisol is the body’s 
primary stress signal,

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and it has a huge range of functions.

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When we experience a stressor—

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anything from a fight with a friend, 
to spotting a bear,

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to an infection or low blood sugar—

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the brain reacts by sending a signal from 
the hypothalamus to the pituitary gland.

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The pituitary gland then sends a signal 
to the adrenal glands.

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The adrenal glands produce cortisol, 
and release some constantly.

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But when they receive the signal 
from the pituitary gland,

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they release a burst of cortisol,

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which spurs the body to generate 
more glucose for energy,

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decrease functions not immediately 
related to survival, like digestion,

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and can activate 
a fight-flight-or-freeze response.

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This is helpful in the short term, 
but can cause undesirable side effects

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like insomnia and lowered mood 
if they last too long.

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Cortisol also interacts 
with the immune system in complex ways—

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depending on the situation,

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it can increase or decrease 
certain immune functions.

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In the process of fighting infection,

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the immune system 
often creates inflammation.

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Cortisol suppresses the immune system’s 
ability to produce inflammation,

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which, again, 
can be useful in the short term.

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But too much cortisol 
can have negative impacts,

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like reducing the immune system’s ability 
to regenerate bone marrow and lymph nodes.

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To prevent levels 
from staying high for too long,

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cortisol suppresses the signal 
that causes the adrenal glands

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to release more cortisol.

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Medicinal corticosteroids channel 
cortisol’s effects on the immune system

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to fight allergic reactions, 
rashes, and asthma.

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All these things are forms 
of inflammation.

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There are many synthetic steroids 
that share the same basic mechanism:

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they enhance the body’s cortisol supply,

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which in turn shuts down 
the hyperactive immune responses

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that cause inflammation.

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These corticosteroids sneak into cells 
and can turn off the “fire alarm”

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by suppressing gene expression 
of inflammatory signals.

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The steroids in inhalers and creams impact
only the affected organ—

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the skin, or the lungs.

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Intravenous or oral versions, used 
to treat chronic autoimmune conditions

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like lupus or inflammatory bowel disease, 
impact the whole body.

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With these conditions, the body’s 
immune system attacks its own cells,

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a process analogous to a constant 
asthma attack or rash.

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A constant low dose of steroids

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can help keep this renegade
immune response under control—

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but because of the negative psychological 
and physiological effects

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of longterm exposure,

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higher doses are reserved 
for emergencies and flare-ups.

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While an asthma attack, poison ivy welts, 
and irritable bowel syndrome

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might seem totally unrelated, 
they all have something in common:

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an immune response 
that’s doing more harm than good.

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And while corticosteroids 
won’t give you giant muscles,

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they can be the body’s best defense 
against itself.