Causes of Chickenpox

Chickenpox is caused by the varicella-zoster virus - one of the most contagious viruses known. Understanding how it spreads explains both why whole households catch it and why it almost always strikes only once.

The virus

Varicella-zoster virus (VZV) belongs to the herpes family. The first infection produces chickenpox; the virus then sleeps in nerve roots for life and can wake decades later as shingles (herpes zoster). One virus, two diseases, a lifetime apart.

How it spreads

• Airborne: coughs, sneezes and even breathing in shared air - the virus floats on tiny droplets
• Direct contact: fluid from the blisters is loaded with virus
• Contagious window: from 1-2 days BEFORE the rash appears until every last blister has crusted over - typically 5-7 days after the rash starts
• Attack rate: around 9 in 10 non-immune close contacts catch it; one schoolchild can seed a classroom

Who catches it

Anyone without immunity: no past infection and no vaccination. In India, where routine chickenpox vaccination is not universal, many adults remain susceptible - and adult chickenpox runs rougher than the childhood version.

Why only once (usually)

Surviving chickenpox leaves durable immunity; second attacks are rare and usually mild or occur in the immunosuppressed. Vaccination gives the same protection without the disease.

What does NOT cause it

Heat, "body heat", eating eggs or chicken, seasonal winds, or a deity's displeasure - none of these cause chickenpox. The virus is the only cause; everything else is timing and exposure. Folklore can decorate care, but isolation and hygiene are what actually protect the household.

One-line summary

Chickenpox is the varicella-zoster virus spreading through air and blister fluid from two days before the rash until full crusting - nearly everyone non-immune nearby catches it, almost nobody catches it twice.