system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do disposable razors with 5 blades not cause razor burn compared to a razor with 2-3 blades?
gpt
Good blades and good shaving practices will usually help you avoid razor burn, moreso than the number of blades.

But generally speaking, pulling, tugging, and scratching are the basic causes of razor burn. This can be on hair or skin.

Friction is one of the main reasons why this happens. While increasing blades increases the friction, it also increases surface area. This increases surface area decreases pressure placed on the skin at any one point of the blade, making it run smoother. Think of using your fingernail to scratch versus using your fingertip. Your nail is much thinner and applies that pressure in one specific spot, whereas your fingertip spreads that pressure over a larger area.

Perhaps the other important reason is that more blades increases the amount of hair that can be trimmed and stuck in the blade, decreasing the need for passing the blade again in the same spot (means less dry skin to blade contact). This also helps the blades to not wear out as quickly (less usage each day).