There are two broad groups of fungi: yeast and moulds.Everyone has heard of fungi. You have probably already seen them on old bread or rotten oranges, you know the fungi in 'blue cheese' and you also know that the mushrooms you find in a forest and oyster mushrooms are fungi.
Fungi can also grow on people. You may think this is strange, but not when you have taken a closer look at the weird and wonderful world of fungi, however.
There are over a hundred thousand different types of fungi and they all need a matrix to extract their building materials. Some require dead wood, others dead leaves, grain, cheese, wallpaper, fruit, nuts, bread, spice powder, etc… Some even grow on people or animals.
Different types of fungi
Some fungi that live on people use the keratin 
in our skin as nutrient. They are known as 'dermatophytes' , which means literally 'growing on the skin'.
Other fungi need sugars or fats. These are known as 'yeast fungi'. There are many different types of yeast fungi. Some yeast fungi allow bread to rise, can be used in the production of beer, others live in humans, however. The most well known are 'Candida' and 'Pityrosporum'. They can cause skin infections and mucous membrane infections.
Some fungi are very aggressive. Infections by 'Aspergillus' occur quite frequently in people with weakened resistance. Actually, Aspergillus can be found everywhere and is harmless to healthy people, but they can be life-threatening to people in poor health. Aspergillus is responsible for infections of the bronchi, less frequent locations are the central nervous system and the gastrointestinal tract.
Threads and spores
Most fungi have a 'growth phase' and a 'reproductive phase'. The mushrooms you see in the forest, are the reproductive form: under the cap, spores can be found that can grow into a new fungus. Under the ground is a system of hyphal threads: the growth form or 'mycelium'.
The fungi that grow on or inside our bodies also have these two forms. These are so small that they are only visible with a microscope.
What you can actually see, feel and smell, are the consequences of this growth, i.e. an irritated skin, a coated tongue or white discharge. The spores can infect other people; therefore fungal infections are a contagious disease.
