People who believe in taking bird’s nest as tonics may have another hazard to look out for.

According to the Deputy Minister of Agriculture in Malaysia, Cai Zhi Yong, red blood bird’s nest is not actually stained red by blood.

He explains that the red colour actually comes from the bird's nest being contaminated by bird droppings.

This phenomenon has led to a black market where unscrupulous dealers artificially create red blood bird's nest by using a preservative made from bird's poop.

This preservative acts as a red pigment which is used to disguise ordinary and cheaper bird’s nest.

The preservative contains hydrochloric acid nitrate that exceeds the acceptable amount for human consumption.

According to Malaysia's Ministry of Health, food must not contain more than 70ppm of the substance, but red blood bird's nest may contain up to 2,220ppm of the toxic chemical.

Local retailers are on the lookout to prevent the import of these dangerous and treated red blood bird’s nest.

An experienced bird’s nest dealer, Lin Ming Jian, says: “This kind of fake treated bird’s nest will not expand after being soaked in water, unlike the real deal which can expand up to 7 – 8 times. The pigment will seep out quickly too.”

Up to 70% of the bird’s nest in Singapore is imported from Indonesia. The rest comes from Malaysia and Thailand.

There are several common beliefs concerning red blood bird’s nest.

One belief is that the swallows spit blood after they eat lotus seeds, and the spit stains their nests red.

Another belief is that the nests are stained red by the minerals from the rock walls that the nests are built on.