How does an increase in pulse duration influence the risk to the epidermis?

• A. Longer pulse duration increases peak power
• B. Shorter pulse duration lowers follicle destruction
• C. Longer pulse duration lowers peak power and can reduce epidermal damage in darker skin, though too long may decrease follicle destruction
• D. Pulse duration has no effect on epidermis

Answer: (C)

The main concept is that pulse duration changes how heat is delivered to skin and hair. Increasing the pulse duration spreads the same amount of energy over a longer time, which lowers the peak power. That lower peak temperature reduces the amount of heat deposited in the epidermis, helping protect darker skin where more epidermal melanin can absorb energy and be damaged. At the same time, if the pulse is too long, there isn’t enough concentrated energy to heat the follicle enough to destroy it, so follicle destruction can drop. So longer pulse duration can reduce epidermal damage, especially in darker skin, but risks reduced effectiveness if pushed too far.