Aldehydes, like acrolein, formaldehyde, benzaldehyde, propionaldehyde or acetaldehyde, are a class of organic molecules that are ubiquist. Smoking is a much higher source of aldehydes than vaping, as demonstrated by several studies and summarized by a very didactic video.
As an illustration, the global production capacity of formaldehyde for industrial purposes was higher than 46.4 million tons in 2012 and is predicted to reach 52 million tons in 2017. Automobile exhaust is a major source of formaldehyde in outdoor air while pressed-wood products are often a source of formaldehyde in homes. Acetaldehyde and butanal are other common aldehydes used by the industry where they are the base of polymers like polyurethanes.
From a structural aspect, the danger associated with this chemical family comes from the presence of a carbonyl group (C=O). Due to its double bound with an oxygen atom, the carbon of carbonyl group is very reactive and can easily bind other atoms to create molecules with other properties like ketones, carboxylic acids and alcohols. Formaldehyde in solution with water, formalin, is a histological fixative that stops the deterioration and decay process in organic tissues. It is commonly used as embalming fluid, lower concentrations in water solution act as a biocide for system disinfection.
Aldehydes also trigger metabolic effects on animals (including humans) that depend upon the route of exposure. Aldehydes are not only irritants for the aerial tract, they also have adverse human health effects, leading to the formation of tumors in the most acute conditions of exposure. Such conditions are met, for example, at the level of the nasal or buccal cavity of a smoker, where the smoke is first in contact.
Some very famous researchers are concerned by aldehydes. Maciej Goniewicz warned about their danger. In response to this concern, Konstantinos Farsalinos carried out complementary studies and revealed the danger associated to dry burns when vaping, a phenomenon that generates a lot of aldehydes, principally acrolein and formaldehyde.
Even if their presence in e-vapor is a subject that motivates anti-vaping advocates, their presence in cigarette smoke has never fed media headlines in a similar proportion, probably because their dangerousness was hidden in smoke by much more harmful molecules. Obviously, this is not the case with e-vapor and only a few molecules are revealed potentially harmful among which aldehydes are the most abundant.