system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What exactly are the moles on your body? Why do we need to go through surgery to actually remove one?
gpt
A mole (or melanocytic nevus) is an often benign local overgrowth of melanocyte cells. Melanocytes are the cells responsible for making melanin, a dark skin pigment. That's why many moles appear brown or dark - the large number of melanocyte cells make lots of melanin, which give the mole its colour.

There are numerous types, some depending on which layer of the skin the cells are from. Usually you're either born with them or you get them within the first 20 years of life, then they tend to stick around.

We go through surgery to remove them for two reasons; either the person with the mole wants it removed for cosmetic reasons, or a doctor suspects the mole may actually be a melanoma - a particularly nasty type of skin cancer.

If there's any indication the mole is a melanoma, it's removed, usually with negative surgical margins, which means you cut out an area of skin around the cancer that contains entirely normal cells (so you can be sure you cut it all out and didnt leave any behind). The removed bit of tissue is then sent off for testing to see if it is anything to worry about or not - that's called a skin biopsy.