Standard commercial shampoos instruct you to "wash and repeat daily." In trichology, this blanket advice is counterproductive. Scalp health requires a customized routine calibrated to two biological vectors: **scalp sebum secretion** and **cuticular hair porosity**.
Vector 1: Calibrating by Sebum Level
Sebum is a natural lipid barrier secreted by the sebaceous glands to lubricate the hair shaft. Overproduction or underproduction dictates wash frequency:
- Oily Scalp (Hyper-secretion): Requires washing every 1-2 days using mild, non-stripping surfactants. Leaving heavy sebum on the scalp leads to lipid oxidation, promoting *Malassezia* fungal colonization and follicle irritation.
- Dry Scalp (Hypo-secretion): Requires washing every 3-4 days. Over-washing strips the fragile stratum corneum barrier, leading to dry scaling and itching.
Vector 2: Calibrating by Hair Porosity
Porosity refers to the hair's ability to absorb and hold moisture, determined by the integrity of the cuticular shingles:
- Low Porosity: Shingles are tightly packed. Warm water must be used initially to swell the cuticle slightly, allowing active nutrients (biotin, caffeine) to penetrate the strand.
- High Porosity: Shingles are lifted or damaged (often from chemical treatments). Requires lukewarm/cool water washes to prevent further cuticle damage. It benefits from lipid complexes to seal the open cuticle layers.
• Water Temp: Never exceed 38°C (100°F). Excessive heat melts lipid bonds holding cuticles together.
• Scalp Massage: Use fingertips only. Avoid scratching the scalp, which can cause micro-fissures and introduce pathogens.
• Drying: Pat dry gently. Do not rub aggressively with a towel, as wet hair has increased friction and is highly susceptible to breakage.