US pharmaceutical companies are luring Mexican residents across the border to sell their blood for up to $400 a month.

The blood donors are using tourist visas to enter the United States and make hundreds of dollars by donating plasma up to twice a week.

Out of a total of 805 blood plasma donating sites in the United States, 43 are located near the southern border.

The border centers generate twice the amount of donors on a weekly basis than the rest of their counterparts in the rest of the country, according to ProRepublica.

Companies, such as Spanish-based Grifols, which operates 17 donation centers along the southern U.S. border, benefit from the Mexicans, whose government banned the selling of blood plasma in 1987.

Four other companies, pharmaceutical companies, CSL, whose headquarters are in Australia, the United Kingdom-owned BPL, and U.S.-based GCAM Inc. operate within the Mexico-United States border.

The American market sits atop the $21 billion global industry.

Gamaliel and his daughter Genesis are among thousands of Mexican who legally cross the United States border with their tourist visas to donate blood plasma and make as much as $400 a month

The Unites States has 805 center where blood plasma is donated and sits atop a $21 billion global industry

A donor from Mexico, identified as Genesis, said that she followed the footsteps of her father and has been crossing the Mexico-Texas border two times per week over the last three years.

The 21-year-old aspiring paramedic, like many other volunteers, is unemployed. She lives in Ciudad Juarez, were an average employee makes up to $9 a day.

Her monthly take home 'salary' as a blood plasma donor almost doubles that she would make working a regular job.

When it comes to being interviewed by a CBP officer at the border entry, she generally says she is visiting a family member in El Paso, Texas, before veering off road and heading to the blood bank center to undergo a process that typically lasts over an hour.

Despite the financial windfall, frequent blood plasma donors could encounter serious health problems as it could damage the immune system.

Some countries strictly limit or ban donating blood plasma in exchange for monetary compensation. However, blood banks in the U.S. are permitted to pay donors the guidelines for tracking their wellness are lax.

Genesis regularly encounters the downside of being a frequent blood plasma donor and constantly complains of fainting, migraine headaches and 'numbness in her limbs.'

In an emailed statement to DailyMail.com, a Grifols representative wrote: ' All donors are subject to the same strict eligibility and safety requirements imposed by the FDA, and must meet our rigorous health screening, quality and safety standards, as well as industry regulatory criteria, to be approved to donate. We are grateful for the time and effort of all our committed donors.'

Mexicans donating blood also reap in on additional incentives if they get friends and family members to join, too.

However, they could lose their B1/B2 visas in the process, according to Jeffrey Quiñones, a spokesperson with U.S. Customs and Border Protection [CBP].

'B1/B2 card holders who cross the border to sell plasma may be in jeopardy of having their document revoked by a CBP officer,' the immigration official told DailyMail.com.

'The CBP officer has discretion and may handle these situations on a case-by-case basis taking into account all available information present at the time of entry.'

When asked if using the visa to get paid for donating blood was a criminal offense, CBP spokesperson Roger Maier told ProRepublica, 'I'm sorry, it's a gray area, but I can't give you a yes or no.'

According to ARD, workers no longer associated with the blood centers said they would advice Mexican tourists to lie to border officials if asked why they were visiting the United States.

The United Kingdom-owned BPL in El Paso, Texas, is one just one of 43 sites that Mexican residents visit to donate blood plasma

'B1/B2 card holders who cross the border to sell plasma may be in jeopardy of having their document revoked by a CBP officer,' a CBP official told DailyMail.com

ARD was able to access documents covering a two-week stretch at five donating centers operated by Grifol and discovered that almost 90 percent of daily donors were visiting from Mexico.

At least 10,000 Mexican residents donated blood plasma during the two weeks thanks to the B1/B2 tourist visa the U.S. Department of State offers after charging a non-refundable application fee of $160.

'I understand it is not illegal,' said Gamaliel, Genesis' 44-year-old father who earns $100 a month operating his own fitness gym and who for the last nine years has donated blood twice a week.

'But, if you get to an officer in a bad mood, they could take your visa. So it's better not to tell.'

According to Gamaliel, the money is deposited into an ATM card, funds that he also uses to support his youngest daughter and buy her food, clothing and toys.