Jackie Nelson, a retired police evidence officer in Ormond Beach, Fla., said she hoped the new rules would eliminate the kinds of obstacles she recently experienced. When she moved from Texas, she said, her doctor there asked her to pay an exorbitant fee — more than a thousand dollars — to provide her with a copy of her medical records.

“People like myself, I’m a senior, I’m on Social Security — I don’t have a thousand dollars to pay for my records,” said Ms. Nelson, who is managing multiple health conditions. She said she hoped the new data-access rules would “stop doctors from withholding” patients’ data and “make the doctor accountable for what they are doing.”

Health regulators are opening patient access to their medical records against a backdrop of a virtual gold rush for Americans’ health data by hundreds of companies. So many entities have access to Americans’ medical records — including identifiable medical data and pseudonymous files that track people by ID codes — that it can seem easier for third parties to acquire patient data than patients themselves.

Dozens of professional medical organizations and health industry groups have pushed back against the rules, warning that federal privacy protections, which limit how health providers and insurers may use and share medical records, no longer apply once patients transfer their data to consumer apps.

“Apps frequently do not provide patients with clear terms of how that data will be used — licensing patients’ data for marketing purposes, leasing or lending aggregated personal information to third parties, or outright selling it,” Dr. James L. Madara, the chief executive of the American Medical Association, wrote in public comments to health regulators last year. “These practices jeopardize patient privacy.”

Dr. Rucker, the health department’s technology coordinator, said the new rules take patient privacy into account. When patients initiate the data-sharing process with apps, he said, their providers will be able to inform them about privacy risks.