Cleaning up mold
After looking up "mold" on the CDC Web
site, Amy’s parents learned that the only way
to remove the mold would be to eliminate
one or more of the ingredients molds need to
survive. As they proceeded with the cleanup,
they wanted to keep their house warm, so
they could not remove the warmth factor
that allows mold to grow. Also, because they
could not eliminate all potential food sources
for the mold, their first step was to remove
as much moisture as possible. They pulled
all of their wet rugs and soggy books out of
the house, and they turned on lots of fans,
but their first floor still smelled musty. So,
they needed to take their mold removal a step
All of the wet materials in Amy’s home
had caused the indoor humidity level to rise.
Humidity is the amount of water vapor in the
air. We feel sticky on hot, humid summer days
because our sweat sticks to our bodies, and
it cannot evaporate easily into the air. Sweat
evaporates mostly when there is not much
water in the air. In a place with high humidity,
there are already lots of water molecules in
the air, so your sweat will not evaporate much
because the humid air cannot hold as many
additional water molecules.
Warm air can hold more moisture than
cool air can, because water molecules move
faster and can maintain a gaseous state more
easily at higher temperatures. In cooler tem-
peratures, water molecules slow down and
condense to form liquid water (Fig. 2).
So, one way to pull water vapor out of the
air is to lower the air temperature and cause
water droplets to condense from water vapor,
which is what cold-coil dehumidifiers do. They
use a fan to pull moist air into a machine that
contains cold metal coils. This rapidly causes
a room’s water vapor to condense and to drip
into a holding bin. The machine then pumps
warm, drier air back into a room. Once air
becomes dry enough, it can begin pulling
moisture out of damp surfaces, such as wood
floors and cabinets.
Coming out of it
After educating themselves about how best
to take care of their mold situation, Amy’s
parents realized that they would need to strip
their entire first floor of all the materials that
were soaked in the flood. This included car-
pets, walls, and furniture.
Luckily, they removed the
materials in time to prevent
serious damage to the
second floor of their house,
which they kept dry with
a dehumidifier for several
months after the flood.
While the flood posed a
serious burden on Amy’s
family, they came out of it
more aware of how mold
grows and the limitations of
mold removal. Luckily for
Amy, her symptoms never
developed into anything
more severe than a runny
nose and itchy eyes, which,
at the very least, made her nostalgic for fun
times in her grandparents’ barn and in her base-
ment playing hide-and-seek with friends.
Mold: Basic Facts. National Center for
Environmental Health, Centers for Disease
Control and Prevention, May 22, 2014:
Thompson, A. Why Is Humidity So Uncomfortable?
Live Science, Feb 20, 2013: http://www.
uncomfortable.html [accessed Sept 2015].
Romano, J. How to Dry Out a Flooded House.
The New York Times, July 9, 2006: http://www.
ik5J6Fj9x56LSgMrhlFWBA [accessed Sept 2015].
Laura Poppick is a science writer who lives
in Portland, Maine. This is her first article in
Figure 2. As the temperature increases (red arrows on top), water goes from ice to liquid water to water
vapor, and as the temperature decreases, the opposite occurs. In a humid environment, decreasing the
temperature causes the water vapor molecules present in the air to condense into liquid water. The red
dotted lines represent hydrogen bonds between water molecules.
How Sweat Evaporates
In order for sweat to cool your body
temperature, sweat must evaporate.
Beads of sweat on your skin are in the form
of liquid water. When the water temperature
rises, the average kinetic energy of the water
molecules increases, and when a molecule
gains enough energy, it can break free
from the intermolecular forces of attraction,
which hold water molecules together, and
evaporates. As water molecules evaporate, their
energy—or heat—is removed from the sweat that
remains on your skin, and this loss of energy cools
the surface of your skin. —Laura Poppick
Ice Liquid Water Water Vapor