The answer is friction. Milady credits this specific massage movement — a deeper, rubbing pressure applied to the skin — with proven benefits to circulation and glandular activity.
Vibration, tapotement (percussion-style tapping), and percussion are all real massage movements with their own uses in facial and scalp treatments, but the textbook attributes the circulation/glandular benefit specifically to friction, not to any of the others.
Milady Standard Barbering, 6th ed. (massage theory chapter): "Friction has been proven to be beneficial to the circulation and glandular activity of the skin."
This is 1 of the real Skin Science questions in FadeJunkie's Milady-sourced 300-question bank. See the Skin Science practice questions page for a fuller sample, or try the Skin Science practice quiz and flashcards for free. A one-time $15 lifetime pass unlocks the complete question bank across all 13 tested topics.
More real Skin Science questions with sourced answers: Which Skin Function Protects the Body From the Environment, What Is a Defining Characteristic of Aged Skin.
Browse every topic on the Practice Question Hub, or see the Texas Barber State Board Exam Guide for the full exam process — required hours, PSI scheduling, and fees.