system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do things hurt more when the temperature is low (e.g., getting hit in the face with a ball)?
gpt
You have little things in your dermis (second layer of your skin) called "thermoreceptors", which is a mechanism that is specialized in detecting temperature.  You have a much greater density of cold receptors than hot ones.  A cold environment causes less blood flow to your skin for obvious reasons, and causes these thermoreceptors to become more sensitive.  Past a certain threshold, this is interpreted as pain.  When you smack your hand, or in your case hit in the face, when it's cold outside, your hand was already sensitive to the temperature, and you just added on the sensory shock of hurting it.  Your brain then is receiving inputs from two different sensors simultaneously, and interprets it as increased pain.