Thousands of Mexicans cross the border into the United States every week on temporary visas to sell their blood plasma to profiting pharmaceutical companies, news agency ProPublica reported.The donors are lured to the US with Facebook ads and flyers promising cash rewards. Some use the payments as their only income and can take home up to $400 a month if they donate twice a week. Multiple incentives are offered as well, including bonuses for recruiting family or friends.Some nations forbid paid plasma donations at a high frequency due to concerns for donor health and quality control. The US allows paid donations and has comparatively loose standards for monitoring their health, according to ProPublica.Donating plasma too often can also be harmful to a donor's immune system. Donors in the US are allowed to give plasma up to 104 times a year, which is much more often than in most other countries. In Mexico, selling plasma has been banned since 1987.Genesis, a 21-year-old Mexican studying to be a paramedic, said that she gives plasma twice a week in El Paso, Texas. She often faints, and gets migraines and numbness in her limbs. "I have trouble lifting stuff, problems with my muscles," she said.A temporary visa allows non-immigrants to enter the US to visit family, shop or "engage in commercial transactions, which do not involve gainful employment in the United States.”At least 10,000 Mexicans cross the border every week to sell their blood plasma, according to estimates by ARD German TV.The United States exports the purchased blood plasma around the world, with Europe being the main consumer. One of the main companies buying blood plasma along the US-Mexico border is CSL, an Australian-owned biotechnology company.Former employees from pharmaceutical companies along the border told ARD that the companies set up there because they know that locals need the money. Those who sell to CSL can even get "reward points."The companies claim that the payments are not wages as defined by law and are instead "compensation" for donor's time. One former employee said that the companies avoid saying that they buy the blood plasma from donors, because that would sound like a "form of prostitution."Genesis told ARD that the staff at the donation centers "don't really pay a lot attention to the people donating... To them, I'm more like a commodity than a patient or donor."The pharmaceutical companies say that they carefully monitor donors, according to ProPublica.Genesis's lab results showed a dangerously low immunoglobulin G level. The loss of antibodies can damage the immune system and lead to serious infections like pneumonia. The doctor who conducted Genesis's blood tests recommended that she stop donating plasma until her body recovers, but she responded that "stopping is a luxury I cannot afford."According to the US State Department, visa rules do not address "“the legality of this specific purpose of travel.”The Food and Drug Administration requires companies to monitor patient health before each donation. In some CSL centers, the payment amount depends on body weight, which determines how much blood plasma can be collected.