LONDON, England -- Manufacturers and pharmacies are reporting a sharp increase in demand for face masks.
The WHO says face masks are useful primarily for people already ill to stop the virus' spread.
Chemists in the UK and in France contacted by CNN said they had been out of face masks since Monday, attributing demand to fears over swine flu.
Several told CNN they were unable to order new face masks as suppliers struggled to cope with demand.
A chemist at British chain Boots in Pimlico, London told CNN: "We usually don't stock them and just order them on demand.
"A customer came in earlier and said he had tried several independent pharmacists in the area but was unable to get a mask.
"We have also not managed to order any masks from our usual supplier."
Anthon Thomas, a sales manager at Crosstex, a medical company that sells masks and other sterilization products, said they had also seen an increase in demand, but he did not think supply would run out.
Bloomberg news reported that medical companies 3M Co. and Alpha Pro Tech were manufacturing more masks and stood to make large profits if the demand continued to rise.
However, the World Health Organization (WHO) is warning against relying on face masks, especially for those not infected with the virus.
"They are mainly useful for people who are already sick, to prevent spreading. Not so much to stop people from catching the virus," Sarah Cumberland of the WHO told CNN.
"At the moment it's a panic reaction. The best thing to do is what you would always do to avoid catching a virus: washing your hands and not bringing your hands to your face," she said.
The UK's Health Protection Agency also told CNN that the use of face masks was not necessary or recommended for protection against the swine flu virus.
In Paris, some pharmacies said they had rarely seen such high demand for the product. "If you find a masks supplier, please send him to me," the chemist at Pharmacie des Halles told CNN. iReport.com: Worried about swine flu?
However, no cases of swine flu have yet been reported in England or France and the WHO judges the two countries as the best prepared to handle an outbreak.
Sales of hand sanitizers have also reportedly seen a rise. CNN iReporter Melissa Fazli commented that her local WalMart in Brea, California, had run out of the product.
Fazli wrote on iReport.com: "According to Ana Cerna, who works in receiving, she has been stocking the shelf all day and quickly selling out of hand sanitizer.
"The $4.50, 40oz GermX is sold out. The $1.98, 10 oz GermX is sold out. I did see a few more bottles at the registers. I did manage to get mine," she wrote. iReport.com: Read Fazli's story