As the United States, Canada and UK welcomes the new year, they seemed to have welcomed a mysterious dense fog too. Those who have posted about it say it has a "burning chemical-like smell". This heavy fog has cloaked parts of the US, and people believe that it is making them sick. What the fog "Feels" like?The mysterious fog was reported after many took to TikTok to share what is happening in their neighbourhood and how the fog is affecting them. David Bamber, 41, who posted about it on TikTok said, "The taste of the air, the only word I can think of is toxic. It’s super weird and it’s kind of worrying me a little bit." He said it feels like "chemicals going down" his throat whenever he breathes. Another TikTok user named Rusky said that he was feeling tired, and had a sore throat and cough. He thinks it is a direct result of the fog. Another resident, told the Daily Mail, that she was out at the gas station and "Within about an hour, I kept sneezing over and over for three hours, and my eyes were really puffy". She said her body felt warm and she felt like she had a fever, and her stomach too was cramping.Another TikTok user Holly Meyer Lucas said that he has been sick and his eyes have been "an absolute painful disasters" for almost two weeks.From all the accounts, it could be said that the fog hit Florida the worst, as these accounts are from fellow Floridian. However, other regions where the fog has been reported are Texas, Wisconsin, Iowa, Minnesota, Virginia, Maryland, West Virginia, Nebraska, Kansas, North Dakota, and Oklahoma. What is the fog sickness?Experts believe that this may be fog, coupled with viruses which have surged during the winters. Furthermore, the tiny water droplets, made from trapping absorbed pollutants smells in the air. The added moisture can enhance the smell.Read more about mysterious fog here. Is it harmful? Why is there a smell?Professor Rudolf Hussar, an atmospheric scientist at Washington University, writes in his article NASA Earth Observatory: "When fog forms, sulfur oxides, nitrogen oxides, and other polluting gases are taken up or ‘scavenged’ by fog water droplets. What’s more, smells become more potent in humid air because the water droplets trap the odor-causing molecules and allow them to linger for longer and remain concentrated." This is the reason why the fog may look grainy, as is shared by some of the TikTok users.In terms of causing harm, moisture is capable of irritating the respiratory system by introducing water to the lungs. This can then trigger symptoms of coughing, shortness of breath, chest pain, congestion, and wheezing. People who have asthma are more at risk.Last year too, near January, a thick dense fog covered the skies of the US and parts of the mid-Atlantic, leaving over 70 million under fog alerts. This is also one of the leading reasons that made the dehumidifier market worth $1 billion in America, last time.Is it fog? Is it something else?There are conspiracy theories that claim that it may be a chemical weapon and has been compared to Operation Sea Spray experiment from 1950. This experiment involved releasing bacteria into the air two miles off San Francisco to assess the vulnerability of major cities to biowarfare attacks. It resulted in 11 people being hospitalized with severe urinary tract infections, one of whom passed away.