SAN DIEGO – A dangerous underground of “pump parties” has sprung up around the country catering to transgender individuals seeking more feminine features through cheap — sometimes deadly — black-market silicone injections, experts say.

Two San Diego transgender women were near death on Friday after unlicensed practitioners injected them with liquid silicone at a “pump party” five days earlier, officials said.

Police are searching for a Los Angeles-area woman suspected of injecting as many as a dozen people at two parties that day. None of those at the second party has contacted police.

The two injured women, aged 30 and 45, are among hundreds, perhaps thousands, of people who have sought the illegal treatments to save money and to avoid dealing with the medical establishment, experts say. Their goal is to make their hips, lips, cheeks and buttocks appear more feminine.

“I’ve been hearing about pump parties for many years but more in the past few,” said Dr. Walter Bockting, the coordinator of transgender health services at the University of Minnesota’s Center for Human Sexuality. “Being beautiful and shapely is very important to certain segments of the transgender community — it’s a self-esteem builder for people who are feeling rejected by their families and communities.” At pump parties, groups of patients typically receive silicone injections from an unlicensed, untrained person who is often using non-medical silicone. Costs tend to run between $200 and $1,000 per treatment, police said.

Industrial-grade silicone, floor products and sealers, and a host of contaminants including motor oil and paraffin have all turned up in post-party patients.

The U.S. Food and Drug Administration has prohibited direct injection of silicone since 1992. Medical-grade silicone now can be inserted into bodies legally only if it is encapsulated in a sac — as in a breast implant — and does not come into contact with tissue.

The black market silicone and contaminants can trigger an immune system reaction that results in respiratory arrest — as happened to the two San Diego women, police said.

There also have been cases of blood poisoning, including a death in Georgia in 2003, and other complications that led to the deaths of three women in Houston and a Florida woman, also in 2003.

Still, some in the transgender community see silicone injection as a reasonable choice and many Web sites offer advice on how to get injections more safely.

“Are you going to trust your best girlfriend or a doctor who may be rude to you and refuse to treat you or disrespect your reasons?” said Mara Keistling, of the National Center for Transgender Equality, in Washington, D.C. “We provide people with advice because we hope to have people do this as safely as possible.”

Doctors warn that there is no safe way to inject silicone.

“We know silicone isn’t safe when it’s not encapsulated,” said Janie Cordray of the Medical Board of California. “We know it migrates, that it often becomes part of the tissue and can’t be removed, that it causes chronic, serious health problems.

“It’s really sad that people can’t wait and have appropriate, safer surgery.”