While cutting a lemon, I discovered something strange inside… and I was amazed when I realized what it was.

Is it dangerous for your health?
Good news: handling this type of lemon is safe. However, eating it is strongly discouraged. Once rot has started, the fruit is unfit for consumption, even if part of it still looks good.
The fungus in question does not cause an immediate reaction in humans, but it can produce potentially irritating toxins, especially if you are sensitive or allergic. Prevention is better than cure.