Recently, I asked for input from some of our readers for topic ideas. The response was wonderful! I never fail to be impressed by the depth of thought you ladies and gentlemen are putting into your selection and usage of hair care products. Many thought-provoking questions and ideas were presented, and I find myself being consistently challenged and sent down interesting scientific avenues. I will be working many of your questions into articles or Q&A format over the next few months and welcome more ideas and questions at any time.
Through the years, I have sensed perhaps a growing frustration amongst the ever-increasingly-informed curly populace. This frustration seems to be rooted in the fact that no matter how much you learn about ingredients, water hardness, pH, water solubility, dew point, etc., there is no one good formula or answer to help you consistently have those perfect, soft and shiny curls that we all so desperately desire. There are reasons for this.
The understanding of the health and behavior of hair is an extraordinarily complicated area of study that involves many different many aspects of scientific study. The topics are highly complex and interdisciplinary and are studied individually in fields such as biochemistry, microbiology, colloid and surface chemistry, water chemistry, polymer chemistry and physics, thermodynamics, meteorology, and even cosmetology. A scientist or practitioner must usually devote many years of their life to just one of these areas to become an expert in it. It is necessary when working in a field related to hair or skin science to delve into other fields and to develop interdisciplinary skills, but generally each of us relies upon our peers in other fields to help us in the areas in which we are not as strong.
In my experience in the field, large companies who spend millions on the research and development of hair and skin care products every year have many facets to their programs. Typically, there are development labs where chemists work on making new products. Those chemists work with suppliers from companies who make and provide raw materials, and they consult with the supplier's chemists and biochemists, who are the resident experts in the individual ingredients. There are microbiology labs, where the growth of organisms are studied and preservatives are tested and refined. There are analytical labs filled with scientists who are experts in testing and understanding the chemical and physical properties of materials, who do testing on hair and skin to see how they are influenced by products and processes. There are groups of engineers who collaborate with the laboratory chemists in pilot plants to scale up development of a product into a manufacturing process. There are quality assurance laboratories, where exhaustive testing is performed on finished products and data is tracked statistically in order to catch products that deviate from the accepted standards. There are also typically experimental hair salons, where volunteers come in and have their hair done and "test" new products and provide feedback on results. (To my knowledge, none of them employ meteorologists!)
My point is that the personal care product industry is a multi-billion dollar one that employs many scientists all around the world for good reason. There just isn't one definitive answer for all of our hair questions and needs. There are too many variables and too many different perceptions of how "good" hair looks and feels. So don't be discouraged if this stuff seems complex, elusive, contradictory, and nonsensical to you at times. Just keep reading up on it, trying different things, and then when you find something that works, stick with it! (until it stops working again, which we all know will happen eventually...)
To kick off, let's address this query from a reader: "We have learned a lot recently about dew point and how it can contribute to the behavior of our hair. Does air temperature play any role? For instance, the dew point could be 40 on a very cold day, and it could also be 40 on a very hot day. Most people have noted that they would not use the same combination of products for those two scenarios, despite the dew point being the same. What accounts for that?"
First of all, allow me to give all of NaturallyCurly's readers kudos for having such a variety of products in your arsenal, combined with sufficient daily presence of mind that you can have different routines depending up on the weather! I desperately need some of you to take me in hand help me out with my own products and routine.
Now, to the question!
The short answer is yes, your hair will behave differently depending upon the temperature to which it is exposed, even if the dew point remains constant. The reason for this is that all materials exhibit a behavior known as thermal expansion, which occurs when they absorb heat energy and experience a subsequent change in volume. This can be a rather complicated process for hair, as it is a biological composite comprised of many different parts.
Last month, we went into some detail describing the complicated composition of our hair (Structure of human hair). You may recall that each human hair is made up of an outer layer of many scales called the cuticle, layers of fatty acids and lipids, and an inner core called the cortex, which is a complicated structure itself. The keratin molecules present in both the cuticle and the cortex, water molecules, and lipids which make up this fascinating biopolymeric composite are all susceptible to expansion and conformational changes due to variations in temperature. Water molecules exist in several different states within a hair strand - as free water, water loosely bound to keratin fibers, and water tightly bound to keratin fibers. Of all of the components of hair, water is probably the most influenced by fluctuations in temperature in the range we typically encounter in the environment.
When hair is exposed to higher temperatures, cuticle scales swell and lift away from the surface of the hair. This creates a much more porous hair strand and also an uneven surface, much more prone to tangling and breakage. Simultaneously, both free water molecules and those loosely bound to keratin molecules in the cortex get excited and begin to expand, causing swelling inside the hair cortex. Eventually, water molecules can begin to diffuse out of the cortex and evaporate out of the hair shaft through the gaps in the cuticle layer.
As water leaves the interior of the hair, the α-helix structure of the keratin protein becomes disturbed which disrupts the crystalline order within microfibrillar structures in the interior of the cortex. In a hot, dry environment, this can mean hair becomes very parched and frizzy. This also means a loss of elasticity, so the hair is more fragile and prone to breakage due to mechanical damage from combing or handling.
In a hot and humid environment, this swelling of the hair opens up the cuticle and allows water from the environment to penetrate the hair shaft, which further increases the swelling of the cuticle and hair shaft. Have you ever walked into a hot environment from a cold one and just felt your hair lift off your head, or started working out in the gym and felt your hair expanding and getting beautifully frizzy as your body temperature went up, or had the frizz set in when you were cooking in the kitchen? All of these phenomena are related to the expansion of hair (and the water within it) due to exposure to heat.
Anyway, to answer your question directly — yes, the temperature is very important. The dew point may give you one piece of information, but the temperature is also extremely relevant. When it comes to hair, especially curly hair, internal moisture, atmospheric moisture and environmental temperature are all very important and interrelated. In my own experience, my hair adores colder weather, and I don't have to put much thought into my routine in lower temperatures, so I put most of my energies into keeping my hair super-moisturized and protected in hotter climates. For me, this means lots of good conditioning product left in my hair after rinsing and the application of a good gel product that helps seal the cuticle and keep it as flat as possible. So far, nothing I have tried is perfect though, especially in Florida heat and humidity!