Monday, April 9, 2012

Seasons are Changing - Dewpoint Visual Aid

Doubtless you have read about dewpoint and what it means for wavy and curly hair. Generally, wavy and curly hair looks better when there is a “just right” amount of water vapor in the air.
The important thing to remember is that we Always Obey the Laws of Thermodynamics! Things tend to come to a state of equilibrium. If there is more heat in your house than outside and you open a window, the warm air rushes out. If you place a glass of iced tea on a table on a hot day, the ice melts and the tea warms as it absorbs heat from its surroundings.©Science-y Hair Blog 2013

Too little water vapor in the air and hair tends to lose moisture to the drier air. Too much water vapor in the air and your hair takes on a lot of moisture and begins to curl more – getting bigger and less defined (frizzing). Just right – and your waves and curls look healthy and defined.

But I need pictures. I love concepts, but for mental recall – flashing back to a picture is so much simpler.

First of all, dewpoint. What you need to know about dewpoint is that is belongs to an air mass. Dewpoint can change with a change in weather, it has trends that go with A) seasons, B) geographic regions. The dew point is the point at which the air is so full of water that it cannot hold any more, so it begins to condense on the grass and anything else sticking up – you have dew. Or fog. Rarely does the temperature go lower than the dewpoint. It’s not supposed to happen at all.  Some air masses (like off a warm ocean) have high dewpoints, meaning the air has to be very warm to get fully saturated with water. Warm air can hold a lot more water than cold air because the air molecules are moving faster. Heat usually does that to molecules. The faster they move, the more they bump into each other. The more they bump into each other, the more the air expands. The more the air expands, the more space there is to pack in – you guessed it – more water molecules!©Science-y Hair Blog 2013

In the morning, when the air is cooler and you have dewy grass you know the temperature went low enough to hit the dewpoint. But the dew evaporates as the day warms up. That is because of dewpoint’s sidekick, relative humidity. If the dewpoint is 50°F and it cools to 50° F overnight, there is dew on the grass in the morning. But when it warms, the air begins to expand and can hold more water – so the water goes back into the air – restoring equilibrium.©Science-y Hair Blog 2013

When dew forms, the relative humidity is 100%. “Relative” in this case means relative to the dewpoint. So we’re always playing off the dewpoint.  The higher the temperature goes, the further from the dewpoint. The further from the dewpoint, the lower the relative humidity.

What you’re meant to recall:
Dewpoint = How much water the air can hold.
Relative humidity= How much water the air is holding right now, at this temperature. Not as important because the water is always there unless the weather changes dramatically.

Now, pictures!!!

Let’s say it’s 68° F (20°C). We’re going to have a box and fill it with 20 “units” (blue circles) of water because at this point, it’s holding all the water it can. Yep, it would be forming dew at 68°F and that’s pretty humid. If your hair is prone to frizzing in humidity, it is either frizzing now, or even going limp (below). I know, it's crooked. Those pesky warm-air water vapor molecules just want to MOVE!
Top: representation of water in the air at
68°F (20°C) dewpoint.
Middle: 50°F (10°C), Bottom 37°F (2°C)

If the dewpoint is 50° F (10°C) then it looks like this (only 10 circles) - second from top, at left. ©Science-y Hair Blog 2013

If the dewpoint is 37° F (2 °C) it looks like this (only 2 circles) - third from top, at left. At this lower dewpoint, wavy/curly hair might be looking a little flatter and less bouncy. See how much less moisture is available to your waves and curls when the dewpoint is lower? Shocking. And I'm not even attempting to "draw" those extremely low dewpoints with tiny fractions of a circle!

Now about that relative humidity. We’re back at a dewpoint of 68°F (20°C). In the morning with dew on the grass, you get this (see the"box" of circles, directly to right).

But later on, it heats up to 85°F (30°C) and all that water is spread out (bottom, right). But it is still there. We never lose matter or energy (water), it just moves around or changes phase (dew to water vapor in the air, it's still water). Hey - thermodynamics again!

We can usually predict our dewpoints in summer or winter (whether you live in the hot, dry desert or temperate, humid summers and dry, cold winters, or some other variation). It’s spring and fall that can be tricky. Temperatures can go up but dewpoints do not follow for warm but very dry spring and fall days. Sometimes temperatures go down while the dewpoint is not yet low (freezing fog, anyone)?
©Science-y Hair Blog 2013
I’ll leave you with this handy “table.” It’s about relative humidity – which varies throughout the day. Watch your local weather forecast (or look at the weather online) to see what the dewpoint and relative humidity are in your area.
At 40% relative humidity, the hair holds close to 8% water
At 50%, the hair holds about 10% water – 40-50% is the “comfort range”
At 65%, hair holds around 13% water – at 65% relative humidity, the air starts to feel “wet” – this is where things start to get frizzy or limp…
At 70%, hair holds close to 14% moisture - your skin and hair are absorbing moisture from the air like crazy!

And this one:
Dewpoints below 50° F (10° C) are “dry.”
In the 50s  (10-15° C) is “comfortable”
60-65° (15- 18° C) is “muggy”
65-70° (18-21° C) is “humid” - if your hair looks best in higher humidity, this is probably your best range.
70° (21° C) and greater is “oppressive” – rainforest-like
The above are from this post.

Dear blog readers:  I hope I'm not "dumbing things down" too much for you. I know most of us are reading things like this when tired or whilst doing other activities. I like to pass information on, not try to impress you with my ability to use jargon. I can write completely unreadable stuff too. But I'd rather write readable things so that people will remember what I wrote and be able to use it...


  1. I love that you explain all your posts with science AND common terms. I don't consider it "dumbed down"at all! I have recently heard about your blog and it is my new hair bible! I started at 2011 and am working my way through all the really great info. Thanks for caring and taking the time to explain the facts AND fallacies of hair.

    1. Totally agree with Jeanne! Thank you! What a shock it must be to be getting messages from this post after all these years! Goes to show once on the net, always on the net. ;)

  2. thank you for your explanation,now i understand.