Every year, millions of people return from vacation with shapelier noses, bigger butts, and tighter stomachs. They are fresh from places like Seoul, where travelers can get free “skin age” analysis in Incheon Airport, and Istanbul, where hair-transplant patients with bandaged heads are a common sight on historic thoroughfare Istiklal Street.

Yet cosmetic surgery is only the tip of the iceberg when it comes to medical tourism, a growing global economic sector in which the wealthy residents of medically impoverished countries and the impoverished residents of countries where health care is astronomically expensive are united in their pursuit of critical treatments abroad. According to the World Health Organization, the industry is already worth more than $100 billion — and it’s set to grow explosively in the coming years.

Why go to the trouble of traveling when you’re already unwell? The numbers speak for themselves: a heart bypass surgery that costs $113,000 in the United States can be had for $20,000 in Singapore, $10,000 in India, and as little as $3,250 in Poland. No surprise that in 2019, an estimated 23 million people went abroad for health care — nearly half of them seeking oncological, neurological, and cardiovascular care.