Fick’s Laws: Mathematical descriptions of diffusion
What is Fick’s Laws?
Fick’s Laws are scientific principles that describe how molecules move from areas of high concentration to areas of low concentration. This movement is the hidden reason your hair can absorb moisture from a conditioner or why hair dye penetrates the strand. Most people miss this: these laws explain why a deep conditioner works better with heat, as warmth speeds up this molecular movement dramatically.
How Fick’s Laws Explain Your Hair’s Porosity
Your hair’s ability to absorb products is governed by Fick’s first law. Think of your hair’s cuticle like a series of overlapping roof shingles. When these shingles are lifted (high porosity), molecules like water and conditioner slip inside easily.
When the cuticle is tight (low porosity), that same movement is much slower. I see this daily in my clinic—clients with low-porosity hair often complain products just “sit” on their hair, which is a direct result of a slow diffusion rate.
Fick’s Laws and The Deep Conditioning Secret
Fick’s second law reveals why timing and temperature are everything for a good hair mask. The law states that the rate of concentration change increases over time and with higher temperatures. Think of it like steeping tea—the longer and hotter it is, the stronger the brew.
Applying a deep conditioner to damp, warmed hair and leaving it on for 20-30 minutes isn’t just a suggestion. It’s a practical application of this law, ensuring the nourishing ingredients have enough time and kinetic energy to diffuse deeply into the cortex. I always tell my patients that a rushed 5-minute mask is like barely dipping the tea bag.
Why Bleach and Color Process Faster on Your Scalp
You’ve probably noticed that color or lightener develops faster at your roots. Fick’s Laws are the reason why. The heat from your scalp acts as a catalyst, accelerating the diffusion of the chemicals into the hair shaft.
Think of your scalp like a warm stove, making molecules move and react more vigorously. This is why I caution against applying the same formula from root to end without adjustment—you risk over-processing and severe damage at the roots where the reaction is naturally fastest.
Fick’s Laws in Your Daily Hair Washing Routine
Even your simple shampoo and conditioner routine is a lesson in diffusion. When you shampoo, you’re using surfactants to help dissolve and diffuse oil and dirt away from the hair and into the water.
When you condition, you’re creating a new concentration gradient of hydrating ingredients aiming to get into the hair shaft. This is why I recommend squishing conditioner into sopping wet hair—the water helps carry the ingredients to the cuticle, kickstarting the diffusion process for better absorption and softer results.
From My Experience
In my practice, I use the principles of Fick’s Laws to create highly personalized hair care plans. For instance, a client with high porosity hair from bleach damage needs heavier, larger molecules that can diffuse in and fill gaps, but they also need a sealant to prevent moisture from diffusing right back out too quickly.
Conversely, for low porosity hair, I focus on using heat and lightweight liquid-based products to overcome the naturally slow diffusion rate. Understanding this science stops the guesswork and allows for targeted treatments that genuinely work, transforming hair from the inside out.
