When viruses infect skin cells, the ensuing immune reaction and destruction of the cells appear as a rash. Rashes can be of different forms, including raised papules, blisters, or just redness over an area of the skin. Different viruses cause different types of rashes.
Viruses are organisms that invade cells and use the cells' protein assembly mechanism to multiply. Viruses are very picky about what cells they infect, usually specializing in one type of cell or tissue. For example, hepatitis viruses infect only the liver. HIV, the virus that causes AIDS, only invades a certain kind of white blood cell. Like the internal organs, the skin is subject to viral infections whose signs appear as a rash.
The skin is made up of a collection of cells in three layers. The outermost layer, the epidermis, is always in contact with the environment, so organisms like viruses and bacteria are always landing on it. Because of the toughness of skin cells, these organisms have a hard time infecting the skin. However, a few organisms penetrate the defenses through hair follicles or through the sweat and sebum glands on the skin.
Smallpox is caused by a pox virus, and the rash it produces is similar to that produced by chickenpox. According to the World Health Organization, Smallpox was eradicated from the world population in the 1970s. However, there is fear that stock of the virus exists in research laboratories, making an accidental or intentional release into the population a possibility. Smallpox is transmitted by respiratory droplets and by the fluid from the rash.
Chickenpox is a common disease of childhood in many countries caused by varicella, a herpes virus. It can occur in adults who have never had chickenpox or a chickenpox vaccination. Although a vaccine is available in the U.S., there are about 10,600 hospitalizations and between 100 and 150 deaths from chickenpox each year, according to Centers for Disease Control and Prevention. The papules (blisters) produced by both chickenpox and smallpox appear as raised bumps with a white, pus-filled head that eventually dries out and falls. The main difference between both rashes is that chickenpox papules are concentrated about the trunk and the face while smallpox papules are heavier in concentration about the arms and legs.
There are two types of herpes simplex virus that cause a rash, blisters, and redness at the site of the infection. Herpes simplex 1 occurs in the mouth and skin of the face. Herpes simplex 2 causes the same kind of symptoms but the rashes and blisters appear more commonly in the genital area. Both are incurable, and both disease may go dormant for months or years before coming back and manifesting themselves as rashes again.
The molluscum virus is also a pox virus, but it does not spread to other parts of the body like smallpox does. It is found in the areas of the skin that came into contact with other infected skin. The virus enters the skin through the hair follicles. The rash constitutes bumps with pus or a white, greasy substance in the middle. It is very contagious from skin-to-skin contact.