There are several different types of skin infection that can affect cats. One example is immune system problems. Another example is infectious diseases and infestations by various types of organisms. Other possibilities include hereditary, developmental, and internal diseases with outward symptoms. Symptoms of skin infections in cats will depend upon which condition is present but will often involve itching, rashes, marks, and hair loss. Treatment will also depend upon the underlying cause. It could involve antibiotics, antifungals, or antivirals if drugs are thought to be needed.
The first type of skin infections in cats to consider is the immune system problems. An example of this is the presence of a retrovirus, such as the Feline Immunodeficiency Virus. This is the cat equivalent of HIV and causes the cat to have a compromised immune system. This makes the cat far more susceptible to skin problems than it would be otherwise. Other immune system problems include hypersensitivity, where inappropriate allergic reactions or autoimmune malfunctions take place.
To most people the most familiar type of skin infection involves infectious diseases and infestations of the cat. This could involve a viral, bacterial, or fungal invader. Ringworm is one common example of a fungal skin infection. Infestations of the cat can involve various species of small creatures such as lice, ticks, and mites. Mange mites are one common problem. These creatures can embed themselves into the skin of the cat and feed from it. In some cases they are big enough to be seen walking across the skin of the animal.
There are three other types of skin infection that could be present in cats. One possibility is that there is a genetic disease causing problems. Another possible problem is that some developmental disorder is at work. Finally, there could be some internal disease that is the underlying cause. In this case the skin infection is just a symptom of some systemic problem. Feline acquired skin fragility syndrome is an example of this.
Clearly there are a great variety of things that can cause skin infections in cats and each problem will have its own set of symptoms to help diagnosis. Most of these conditions are going to pretty itchy for the animal and may involve hair loss, pain, bleeding, and lesions. In each case a different approach to treatment will be required such as antibiotics for bacterial infection, anti-fungal medication for ringworm, or a general anti-parasitic drug for mange mites.