Magic Infections

Throughout the world, magic can run wild, as it is a natural energy that lives within all creatures. However, there are some places where magic energy can gather, either through simple randomness, or through large events like massive battles, where the energy of living beings are released all at once. This processes created what are called Magic Infections, where a specific area becomes concentrated with Magical energy and gains various properties. This can mean a variety of things ranging from strange random magical effects happening in the area, creatures popping into existence from out of nowhere, and many other effects. In the case of battles for example, the magic can concentrate in a way where the dead can be filled with magic and come back as undead, or it can cause those bodies to have magical properties instead. 
On top of this however, it is very dangerous to be in these areas, because of how weak the physical reality of them are, meaning magic creatures from other dimensions can try to enter through them, and worse case scenario created a tear in reality, allowing more creatures from the dimension to enter.
There are however also opposite areas to this, known as Dead Lands. These are zones where no life lives, and anyone who enters them immediately feel uncomfortable or nauseous. These zones swallow up magical energy causing spells to become useless, and creatures that are made of magic are caused terrible pain due to this and can actually end up dying if in one too long. These are the strangest infections, as they don't seem to be caused by anything, they seem to just appear randomly, and then disappear randomly, with any known cause.

Manifestation

It can be manifested in reality in many ways as mentioned, and a lot of the time there is no explanation for it, as many areas can be found out in the wild ranging from thick jungle to dead wastelands, there is very little rhyme or reason to it. However, in general its pretty easy for any living beings to detect these areas, due to the influence of the magic, which one can feel very fundamentally, as all creatures have magic within them. Other than that, one can generally see it through other ways such as through the different symptoms of an infection.

Type

Metaphysical, Arcane