Tuesday, July 23, 2013

Hair Swelling in Water

This subject came up recently on the Wavy Hair Community and I wanted to do a little research to find out how much water is too much - and for how long.
©Science-y Hair Blog 2013
Hair does not take on water immediately, it is designed to repel water in it's unaltered state. Whenever I put hairs in water to photograph them, they do not swell dramatically to the point at which the cuticles are standing up and things look awful. The measurements you'll read about below are tiny. Your hair is probably more protected than the hair cited below by things like conditioner, hair gel and maybe oils - including those that protect your hair naturally. There are 2 ways to get hair to swell with water - expose it to high relative humidity and soak it in water.

When hair begins to swell with water, the swelling is initially distributed along the length of the hair and hair can actually increase in length (temporarily) as a result. But not very much. Think of the pressure exerted on a garden hose when the end is open and water is flowing freely.

When hair is maximally swollen, the pressure of the water strains against the perimeter of the hair shaft. Imagine garden hose in which the "open" end has been plugged. Swelling creates an increase in diameter.

Hair takes on water in high humidity, this causes swelling. At 40% relative humidity, hair can increase in diameter by 5%. At 60% relative humidity swelling can be 7%. When the relative humidity is 100%, hair can increase in diameter by almost 14% because it has taken on water from the air around it.

Things which dramatically increase swelling of hair (much more than water alone): sodium lauryl sulfate, thioglycolic acid (perms), other detergents when concentrated, high pH solutions. Glycerin actually causes less swelling than water!
©Science-y Hair Blog 2013
Swollen hair has several problems. One is that swelling increases pressure and pressure tends to strain tissues. Strain after strain weakens hair over time. Swollen hair's increased girth means that the cuticles stand out - as though you glued tiny shingles on a balloon and then blew it up. That allows water into areas which should be protected by the cuticle. Swollen hair gains weight as well as girth. This causes it to either express its curliest version of itself if the curl is strong (then the curls lose definition to poufy frizz), or go limp when curls are present but not strong relative to the weight of the fiber+water.

Swelling and loss of proteins:
The area just beneath the hair's protective cuticle layers or "endocuticle" of hair may be the area most prone to swelling. It is also loaded with water-soluble, polar -therefore water-attracting- amino acids. It is covered by the membrane-like exocuticle and the sebum from your scalp, both of which provide water and chemical resistance, but both of which are also subject to chemical and physical degradation. In other words, when you get your hair wet, you lose amino acids (protein) from your hair.

How long is too long?
One study published in the Journal of the American Academy of Dermatology tested caucasian hair, African hair and Asian hair swelling when soaking in water vs. time. By about 150 seconds all hair had reached its maximum swelling. That's less than 2.5 minutes in water! Note: The authors did not mention whether the hair had been washed prior to testing, or had any other treatments. I think it's safe to assume it was washed first.
©Science-y Hair Blog 2013
Heat, water and oils:
Water alone does not remove oils. Water and oil do not mix! But oils are not all the same. Oils from your scalp, oils you apply to your hair (including conditioners) can be more-or-less solid at room temperature. Many oils from your scalp and in conditioners have high melting points - coconut oil is an example. Heat can melt certain oils. If they can be melted, they are more likely to be removed with any sort of detergent (even cationic ones) and they are more likely to be carried away with water if possible. Especially if combined with a long soak in which some of the oils might find their way free of the hair. This is why warm to hot water cleans greasy stains better from laundry. 

What can you do to reduce water-damage?
  • Use emollients like coconut oil or other hair-penetrating oils to help make your hair more water-repelling to slow the movement of water into the hair. Conditioners may also be helpful. Here is a post with pictures of hair protected by various oils and conditioners in chlorinated (and high pH) water).
  • Use not-hot (lukewarm or cool) water for washing your hair. Your skin likes that better too.
  • Keep the amount of time your hair is in the water to a minimum. By the time you've been in the water for 2 minutes, your hair has swollen as much as it can. But I think you have a little more time than that, thanks to hair gel, and conditioners which form a film on the surface of your hair.
  • Wash your hair as infrequently as you can stand. The oils from your scalp are well-suited to keeping your hair healthy and hair is designed to repel water by itself if it is not damaged or over-handled.
  • Reconsider bleaching and highlighting and other chemical processes. These treatments make hair more porous - so it takes on water sooner. These treatments also erode the epicuticle, leaving your hair with less natural protection. If you do these to your hair, take extra steps to avoid getting waterlogged.
I don't know about you - I may have to start leaving my hair dry until the end of the shower. And I take fairly quick showers! 

2003 Current research on ethnic hair
Journal of the American Academy of Dermatology, 48 No. 6
A. Franbourg, P. Hallegot,  F. Baltenneck, C. Toutain,and F. Leroy

Chemical and Physical Behavior of Human Hair 
Robbins, 1994. 3rd Ed. Springer-Verlag, New York


  1. Hi WS, I put some oils on my hair and mist it with water and placed a plastic cap over it & left it on for 24 hours. When I took it off my hair was still wet or moist, do you think my hair swelled by keeping it in that environment for that amount of time?

  2. Hi WS, I love your blog. I have a question regarding hair swelling and humidity. I have generally low porous, resistant hair that is medium/fine and about 1b straightness. Almost nothing affects it. However, I recently moved to a tropical climate (dew point over 60 F) and noticed that my hair tends to have more body and almost a hint of curl (like, the idea of a curl). To the point where even my husband commented "Wow, why does your hair look so good?" (lol thanks, jerk!).

    Anyway, as someone who has always longed for more volume and the ability to come close to a beachy wave, what can I do to amplify this effect? I thought the answer was to get my cuticle to retain more moisture, to swell, but you're saying that such an effect is actually damaging and undesirable, correct?

    Is there anything I can do to play up this volume in humidity without significantly damaging my hair? Thanks.

    1. Hello Julia, My hair loves tropical humidity too. Styling products that provide some light hold might be helpful. I'm hesitant to steer your towards saturating your hair with gel and other products because lightness and buoyancy are what is so lovely about hair in high humidity. A styling foam or mousse might help with definition and add a little support - but if you comb it in, you will probably pull out the wave. Spread it lightly over your palms and lean sideways and gently grasp sections of your hair like it is a rope to apply - then once you've done that, "scrunch" the ends upwards to encourage a wave. Definition means the ability to see a distinct wave pattern - curves. You can go all over the price range with mousses and foams - OGX Coconut Curls Mousse, DevaCurl Volumizing Foam, Dippity-Do Girls with Curls Curl Boosting Mousse, Kenra Curl Glaze Mousse 13, Moroccanoil Curl Control Mousse.
      Lighter-weight gels or "serums" that aren't thick and sticky might help with definition and light hold such as: Bumble and Bumble Multi-Talented Sculpting Medium, It’s A 10 Miracle Hold Gel, Kenra Curl Control Gel 10, Ouidad Climate Control Gel, CURLS Goddess Glaze.
      I listed mostly products that have "humidity resistance" built into some of their ingredients because high humidity tends to cause some products to work poorly (lose hold and definition), and that's not what you're after.
      - Once your hair is dry with any sort of product in it - there may be a little bit of crunchy cast, or the hairs may be sticking together more than you might like. Squeeze and massage the hair to break that up. You can even comb lightly - like one would use a pic to loosen curls rather than combing vigorously through.

      If that's all too intimidating, or you hate how products feel - try a leave-in conditioner. Apply it with a splash of water added (pour some over, or duck your head under the shower spray) to help dilute and distribute the product. A product with a little Hydrolyzed protein might be good some days - proteins tend to help with support in any weather. Best wishes - W

  3. Hi WS I have a question regarding LP and volume; I'd like to add more volume to my LP hair and thought the answer was to get the cuticle to swell and try and attract as much moisture as possible to plump it up. I was inspired to take this route after discovering my normally limp and resistant hair has gained body in a tropical (hot and humid, dew point 70+) environment However, you're saying such an approach will eventually cause breakage.

    Is there a way to add "artificial shingles" to the cuticle for a similar effect without compromising my hair's natural integrity? Thanks for your insight.

  4. Thanks so much for the info! I wanted to add that polar and non-polar molecules don't repel each other. Rather, polar molecules are so much more attracted to other polar molecules that they can't be bothered with non-polars. It's kind of like holding a magnet up to a wooden table. Polar molecules have positive and negatively charged ends. Opposites attract, likes repel, and there is no interaction between a charge and a neutral (i.e. the non-polar).