Dr. Kligman is credited as being the first dermatologist to show a link between sun exposure and wrinkles. He coined the term "photoaging" to describe skin aging caused by the sun.

In 1967, he patented Retin-A, a vitamin A derivative known generically as tretinoin, as an acne treatment and received a new patent in 1986 after discovering the drug's wrinkle-fighting ability.

As the architect of the experimental research program at Holmesburg Prison in Philadelphia from 1951 to 1974, Dr. Kligman directed and performed hundreds of experiments on prisoners. In a 1966 interview with the Philadelphia Inquirer, he said of his first visit to the city prison: "All I saw before me were acres of skin. I was like a farmer seeing fertile field for the first time."

The experiments included the testing of mind-altering agents, dioxin and "skin-hardeners" to protect skin from the effects of toxic chemicals. Many were performed under contracts with pharmaceutical and chemical companies, cosmetics firms, federal agencies and the military.

At the time, prison experiments were common. The Holmesburg prisoners were paid for participating, sometimes hundreds of dollars.

Medical testing at Holmesburg took place until 1974, when it was banned by the city amid congressional hearings into medical experimentation, including Tuskegee University tests that infected black men with syphilis. A few former inmates sued the university and the city in 1984, settling for sums of $20,000 to $40,000.

In 2000, soon after a book on the Holmesburg experiments was published, nearly 300 former prisoners sued Dr. Kligman, the University of Pennsylvania, Johnson & Johnson and Dow Chemical, alleging that the experiments caused debilitating health problems. Courts ruled that the statute of limitations had expired.

Dr. Kligman never wavered in his defense of the experiments, insisting that the test subjects did not suffer any long-term harm and maintaining that the research should not have been halted because of the scientific advances it might have yielded.

"The whole thing is so preposterous," he said in a 2003 interview in Dermatology Times. "It gets brought up every few years and the explanations have to start all over again." Dr. Kligman wrote more than 500 research papers and many books during his career, which continued into his later years, and was featured in the New England Journal of Medicine and the magazines Time, Life and Seventeen.

Dr. Kligman was born in South Philadelphia in 1916 to Russian immigrants. He credited much of his success to childhood involvement in the Boy Scouts. Field trips to the countryside with the Scouts fostered a love of plants that led him to botany and indirectly to dermatology.

He graduated with a bachelor's degree in botany in 1939 from Penn State, where he also was a competitive gymnast. At Penn, he followed his 1942 doctorate in botany with a medical degree in 1947.

At the start of World War II, the federal government asked him to travel to South America in search of botanical sources for a malaria- and mosquito-fighting insecticide for soldiers in the Pacific. When the trip was abruptly canceled, Dr. Kligman attributed it to his membership in the Communist Party.

In a 1992 interview with American Health, he said that he was "extremely liberal and idealistic" at the time and that "it seemed that in the Soviet Union, justice prevailed and bigotry had been abolished." Reeling from the rejection, he enrolled in medical school and specialized in dermatology because of an interest in fungal diseases.