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