According to a 2010 study by Karlstad University, the concentrations of PGEs (counted as the sum of propylene glycol and glycol ethers) in indoor air, particularly bedroom air, has been linked to increased risk of developing numerous respiratory and immune disorders in children, including asthma, hay fever, eczema, and allergies, with increased risk ranging from 50% to 180%.
It also contains the following other ingredients: Dicalcium phosphate, microcrystalline cellulose, croscarmellose sodium, stearic acid, silica, magnesium stearate, and film coat (hypromellose, hydroxypropyl cellulose, polyethylene glycol, propylene glycol, titanium dioxide, FD&C yellow #6 lake, riboflavin, FD&C blue #2 lake).
In the 1940s and early 1950s, further studies showed inactivation of diverse bacteria, influenza virus, and Penicillium chrysogenum (previously P. notatum) mold fungus using various glycols, principally propylene glycol and triethylene glycol.
The secondary loop is typically made of High-density polyethylene pipe and contains a mixture of water and anti-freeze (propylene glycol, denatured alcohol or methanol).