Since there are many different types of rashes and just as many different things to trigger them, from allergies to serious illnesses, there’s no one universal way that a rash can spread. Instead it varies by the cause of the rash and how it presents itself. Many do have common traits though.
Some illnesses that manifest themselves as rashes, including scarlet fever, measles and small pox, can be spread through the air when an infected person coughs, sneezes or sometimes just breathes. This makes these illnesses very highly contagious. Luckily, there are vaccines available for many of them.
By contact with an infected person
Other rashes, like ringworm or shingles, are usually spread by touch. This is because the fungus, virus or bacteria that’s causing the rash can move from one host to the other on the surface of the skin. To prevent this from happening, people with these kinds of rashes need to bandage the infected areas of their bodies or stay isolated until they have completely recovered.
By contact with a plant or insect
There are three major rash causing plants present in the United States: poison ivy, poison oak and poison sumac. These plants have a toxic substance on their leaves and stems, called urushiol, that can cause severe skin reactions. Once you rinse the urushiol off your skin, the rash is no longer contagious although some irritation may still show up days later. Some insects, including many types of spiders, excrete a toxin when they sting or bite that is meant to stun prey. This leads to those itchy, nasty bug bite rashes.
Although technically scratching falls under the category of direct contact, it’s actually somewhat different. No one else is likely to scratch your rash for you, but scratching it yourself can cause it to spread to further areas of your body. There are two reasons for this. One, you when you scratch your skin, you are realizing histamine, which tends to make even the healthy skin red and inflamed. Secondly, say you scratch a rash on your arm and then touch your nose. You can expose your nose to whatever fungus, toxin or allergen caused your rash. So when you have a rash, wash your hands often.
Many rashes can spread in more than one way. For example, chicken pox is contagious both in the air and by direct contact with blisters. If you or a family member has a rash, it’s best to ask a doctor what the best way is to contain it.