Videos and images of the aftermath of the attack on the rebel-held town of Khan Sheikhoun circulated widely on social media, prompting many to take action in solidarity with the victims.
Many on Facebook and Twitter changed their profile pictures to a plain yellow colour, symbolising toxic gas.
Some shared an illustration of the toxic sign on a yellow background with "chemical massacre in Syria" written underneath.
Others shared an illustration of a black silhouette of dead children held up by toxic balloons.
"The colour yellow is now being used for profile pictures to advocate for awareness on the current situation in Idlib of Syria," Syrian journalist Rami Jarrah said in a Facebook post on Tuesday.
The hashtag #SyriaGasAttack quickly gained traction on Twitter.
"Praying for every man, woman and child who's lost loved ones in this horrific attack #PrayForSyria #SyriaGasAttack," one user said on Twitter.
Another user wondered "Why are they still calling it an 'alleged' chemical attack?"
Some wondered why many remain unconcerned by the attack.
"#SyriaGasAttack terrifying visuals. If only this was some other country, this sub would be ablaze on social media. Even Syrian lives matter," a user said on Twitter.
"Our lack of action in #Syria is despicable. Children are dying every day. We'll look back ashamed of this part of history," another user said.
Last year, many social media users turned their profile pictures to a red colour, symbolising the blood of the victims of bombardment at the hands of Bashar al-Assad's forces during the brutal siege of Aleppo.