I wouldn't always call it a phobia, they look unnerving to me too. The way I've always interpreted it is that it looks like and reminds us of an infected pimpl

I wouldn't always call it a phobia, they look unnerving to me too. The way I've always interpreted it is that it looks like and reminds us of an infected pimple/abscess/parasite/something growing under the skin where it shouldn't be, coupled with enough empathy or imagination to picture it happening to us. The natural reaction is then disgust and aversion. It's just a result of the way our brains are built, similar to seeing faces where they don't exist. I'm pretty sure I've seen a lotus seed pod in real life and didn't have a reaction, since it's much easier to construct a mental image of what it really is instead of what it might be.