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

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

and shots to ease inflammation.

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

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

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

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

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

rather than shared effects on the body.

Steroids can be naturally occurring 
or synthetic,

but what all steroids have in common 
is a molecular structure

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

arranged in three hexagons 
and one pentagon.

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

though most also have side chains—

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

Steroids get their name 
from the fatty molecule cholesterol.

In fact, our bodies make steroids 
out of cholesterol.

That fatty cholesterol base 
means that steroids

are able to cross fatty cell membranes 
and enter cells.

Within the cell, they can directly 
influence gene expression

and protein synthesis.

This is different from many other types 
of signaling molecules,

which can’t cross the cell membrane

and have to create their effects 
from outside the cell,

through more complicated pathways.

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

Back to the steroids 
in anti-inflammatory medications:

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

Cortisol is the body’s 
primary stress signal,

and it has a huge range of functions.

When we experience a stressor—

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

to an infection or low blood sugar—

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

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

The adrenal glands produce cortisol, 
and release some constantly.

But when they receive the signal 
from the pituitary gland,

they release a burst of cortisol,

which spurs the body to generate 
more glucose for energy,

decrease functions not immediately 
related to survival, like digestion,

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

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

like insomnia and lowered mood 
if they last too long.

Cortisol also interacts 
with the immune system in complex ways—

depending on the situation,

it can increase or decrease 
certain immune functions.

In the process of fighting infection,

the immune system 
often creates inflammation.

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

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

But too much cortisol 
can have negative impacts,

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

To prevent levels 
from staying high for too long,

cortisol suppresses the signal 
that causes the adrenal glands

to release more cortisol.

Medicinal corticosteroids channel 
cortisol’s effects on the immune system

to fight allergic reactions, 
rashes, and asthma.

All these things are forms 
of inflammation.

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

they enhance the body’s cortisol supply,

which in turn shuts down 
the hyperactive immune responses

that cause inflammation.

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

by suppressing gene expression 
of inflammatory signals.

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

the skin, or the lungs.

Intravenous or oral versions, used 
to treat chronic autoimmune conditions

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

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

a process analogous to a constant 
asthma attack or rash.

A constant low dose of steroids

can help keep this renegade
immune response under control—

but because of the negative psychological 
and physiological effects

of longterm exposure,

higher doses are reserved 
for emergencies and flare-ups.

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

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

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

And while corticosteroids 
won’t give you giant muscles,

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