Many people recognize chickenpox for its characteristic itchy, blistering rash. But a number of other conditions can also cause a rash like chickenpox. Similar rashes can occur with shingles, smallpox, herpes simplex virus type 1 or 2, coxsackie virus, echovirus and rickettsialpox. Doctors use certain features of the rash to distinguish a rash like chickenpox from a rash actually caused by chickenpox.
Chickenpox causes small fluid-filled blisters that appear on patches of red, raised skin. These patches can range in size from a pencil eraser to a dime. Initially the blisters are filled with clear fluid, which gives them the appearance of a "dew drop on a rose petal." The blisters eventually burst and develop scabs. New groups of blisters continue to appear over the course of 2 to 4 days, producing a rash with lesions at different stages of development. The blisters seen with herpes simplex and smallpox are about 2 to 3 times larger than those of chickenpox.
Chickenpox usually starts on the face and scalp and then moves to other body areas. Blisters tend to cluster near the midline of the body, with fewer lesions found towards the periphery. Coxsackie viruses can cause a similar rash but the blisters occur mainly on the hands, feet and mouth, producing "hand, foot and mouth disease."
Shingles is caused by reactivation of the chickenpox virus, which remained hidden in the body after causing chickenpox when the person was younger. Shingles occurs as a wide strip of blisters, following the path of a single nerve. Pain is often prominent with shingles. Rashes due to herpes simplex viruses also usually have a limited distribution. Type 1 generally produces cold sores around the mouth and type 2 typically causes genital lesions. Occasionally herpes simplex produces a more widespread rash, particularly in people with an impaired immune system.
Chickenpox often causes a mild flu-like illness that includes a fever, headache, body aches and poor appetite. These symptoms may appear 1 to 2 days before the rash. Adults are often hardest hit, while young children may have minimal or no symptoms beyond a rash. People with hand, foot and mouth disease generally have a sore throat and fever in addition to the rash. Occasionally, the blistering rash of echovirus is accompanied by meningitis -- inflammation of the tissue covering the brain and spinal cord. Meningitis is potentially life-threatening and causes symptoms such as a stiff neck, sensitivity to light, confusion and drowsiness or coma.
Chickenpox is very contagious, being spread by touching an open blister or breathing in virus particles released from a blister. The disease usually develops 10 to 21 days after contact with an infected person. A person is contagious from 1 to 2 days before the rash appears until all blisters have scabbed over. Touching an open blister of a person with shingles can also transfer the chickenpox virus.
Rickettsialpox is a possibility in people exposed to mice, as the disease is carried by ticks that primarily feed on mice. In an addition to the chickenpox-like rash, rickettsialpox is characterized by a "herald spot" at the site of the tick bite. This begins as a red area and later develops into a painless black crust called an eschar. Smallpox no longer occurs as a disease in nature, but its continued existence in laboratories has spurned fears that it could be used for bioterrorism.
Receiving the chickenpox vaccine clearly reduces the chances of developing chickenpox, but no vaccine is 100 percent effective. If the disease does occur, it is generally less severe than normal. Indeed, the presence of just a small number of blisters suggests that a rash like chickenpox actually is chickenpox if the person has been vaccinated. For adults who had chickenpox in the past, the shingles vaccine reduces the chances of developing shingles.
Reviewed by Mary D. Daley, MD.