The keyword 'Trump sniffling' is trending on social media.

The keywords "Trump sniffling" or "sniffling" were the most shared on social media during the live debate between US presidential candidates Trump and Clinton.

The moment Republican presidential candidate Donald Trump sniffed during the debate with opponent Hillary Clinton. Photo: Reuters.

Following the keywords "debate," "sniffing" and "Trump sniffling" were among the most followed and shared terms on Twitter in the US today, according to CNN.

"Why is he sniffling so much? Is he suffering from Parkinson's? Or pneumonia? Brain damage?" Australian writer Caroline Overington wrote on Twitter, according to AP.

"Sniff sniff sniff... Is Trump living in the 80s? Why does he keep sniffling while preparing for debates?" Joy Karley, a biomechanics graduate and gymnastics coach, questioned on Twitter.

Memes of Trump holding a tissue to blow his nose also flooded Twitter.Some people suggest that Trump's runny nose is due to pneumonia, similar to Clinton's a few weeks ago when she attended a memorial service for the victims of the 9/11 attacks in New York.

Many others suggest he may have allergies. Earlier this month, on the "Talk with Doctor Oz" show, Trump said he had had fevers in the spring and fall, but that was nothing unusual as he gets older.

One person speculated that Trump might have used a nasal rinse bottle right before the debate, while others suggested he should rinse his nose for comfort.

According to VNE