The Centers for Disease Control and Prevention on Friday warned people not to use vaping ingredients bought on the street, and to stop modifying either nicotine or cannabis e-cigarette devices, in an effort to curb the vaping-related lung sicknesses that have alarmed health officials in more than two dozen states this summer.

Despite the lack of evidence pointing to a single flawed product or device common among many of the patients suffering respiratory problems, the agency took the unusual step of issuing several recommendations — including telling people worried about their health that they should not even use e-cigarettes and should consult a doctor if they are trying to quit smoking.

In addition, the C.D.C. said: “E-cigarette products should not be used by youth, young adults, pregnant women, as well as adults who do not currently use tobacco products. If you use e-cigarette products, monitor yourself for symptoms (e.g., cough, shortness of breath, chest pain) and promptly seek medical attention if you have concerns about your health.”

The number of reported cases of severe respiratory illnesses totals 215 people in 25 states since late June, officials said. Many have been hospitalized, some with lingering lung problems that required use of a ventilator or extensive monitoring in intensive care units.