As per WHO, over 500 people may have been affected by a suspected chemical attack last week on Syrias rebel-held town of Douma.

The symptoms included respiratory failure, severe irritation of mucous membranes and disruption to the central nervous system. WHO said more than 70 people taking shelter in basements reportedly died in the attack, with 43 of those deaths related to symptoms consistent with exposure to toxic chemicals. Two health facilities were also affected. WHO demanded "immediate unhindered access to the area" and said it was on standby to provide assistance to those affected, as soon as access was granted.

Helicopters also dropped barrel bombs filled with toxic gas on the last rebel-held town in Eastern Ghouta.

Traditional chemical agents can be pulmonary agents (chlorine or phosgene), “blood” agents (cyanide compounds), vesicants (blister agents), nerve agents, and the anticholinergic agent (BZ).

Chlorine is a yellow-green gas with a characteristic chlorine odor, whereas phosgene is a colorless gas or white cloud with odor of newly mown or musty hay, grass, or corn.

Signs of upper airway (central compartment) irritation are consistent with type I (hydrogen chloride or hydrogen fluoride) or combination (chlorine) pulmonary agent exposure. On the other hand signs of pulmonary edema (peripheral compartment) suggest type II pulmonary agent exposure (phosgene).