Image caption A woman in Los Angeles has a Vampire facial in which her own blood is injected back into her skin.

A HIV scare linked to so-called vampire facials at a US spa has slapped a major health warning on a procedure beloved by celebrities and athletes.

Two customers at the New Mexico salon last year have been infected with the virus that can cause AIDS.

Vampire facials involve extracting the patients' blood, separating the plasma and then re-injecting it into the skin.

But there is considerable debate over whether the beauty fad's purported rejuvenating benefits are genuine.

What happened at the New Mexico spa?

Two customers who attended the VIP Spa in Albuquerque between May and September 2018 have contracted HIV, according to the New Mexico Department of Health (NMDOH).

The state agency's investigation found the two had recently contracted the same virus, "increasing the likelihood that the two HIV infections may have resulted from a procedure at the VIP Spa".

Former clients of the now-closed salon are being offered free HIV checks, and more than 100 people have been tested so far.

"NMDOH is reaching out to ensure that testing and counselling services are available for individuals who received injection-related services," said the agency's cabinet secretary, Kathy Kunkel.

Why are vampire facials fashionable?

A vampire facial or PRP (platelet-rich-plasma) treatment is a procedure that aims to use a patient's blood to trick the body into healing and repair.

The blood is extracted and then undergoes a spinning process to separate the plasma, which is injected back by puncturing the skin using a micro-needle.

The theory is that this helps to reinvigorate the skin, making it tighter and smoother.

Image copyright ROLEX DELA PENA Image caption Blood samples are placed in a centrifuge machine

A 2004 study in the Journal of Plastic and Reconstructive Surgery found that extracting plasma by centrifuging leads to the release of significant levels of proteins which may promote wound healing and collagen growth.

PRP treatments have been used for some years in the fitness industry. The American Academy of Orthopaedic Surgeons says elite sports stars like Tiger Woods and Rafael Nadal have used it to aid injury recovery.

In recent years the treatments - which cost around $1,300 (£1,000) - have also become increasingly common in the beauty industry, attracting celebrity endorsements.

The idea of a spa treatment that harnesses the body's own resources instead of injecting drugs or fillers appeals to fans of vampire facials.

The potential for a scary-cool Instagram snap is probably also seen as a bonus.

In 2013 Kim Kardashian had a vampire facial in an episode of the TV show Kourtney & Kim Take Miami. She posted a picture of her blood-covered face to her Instagram page.

There have been hundreds of published medical research papers and trials that suggest PRP treatments have been effective in treating some sports injuries, acne, eczema and other skin conditions.

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Are vampire facials safe?

Vampire facials are available across the US and Europe at many cosmetic surgery and dermatology clinics, which insist they are safe when carried out by qualified medical experts.

The Food and Drug Administration (FDA), a US government regulator, has cleared some medical devices used in PRP procedures, but has not approved the treatment for cosmetic use.

Beverly Hills plastic surgeon Dr Lawrence Koplin says: "These facials are not FDA-approved because the injection of platelets into the skin for the purpose of improving the skin appearance is 'off-label' and not proven to be effective.

"There are not reliable studies showing that platelets are useful in healing tissue, and PRP's original function as a sports injury therapy has still not been proven effective."

In addition there is no standard regulation applying to all states about administering such procedures.

The treatment can be offered at beauty salons without a qualified medical professional present.

In a statement the Cellular Medicine Association founded by Dr Charles Runels, the originator of the vampire facial, said the providers of the treatments in New Mexico were "imposters" who were not on their list of certified practitioners.

"Qualified medical professionals handle blood all day long without serious problems and this procedure is even safer since it's done with the patient's own blood," it said. "But done improperly, people can be killed by cross-contamination.

"Someone using the name to trick people is exactly like someone making a fake Tylenol bottle and putting poison in it," the statement added.