LAS VEGAS (KLAS) — It can be difficult to differentiate between a food allergy and food intolerance – with holiday meals around the corner.

It’s best to know what foods to need to stay away from.

8 News Now connected with a food intolerance expert regarding symptoms, reaction times, and age range.

Dr. Jill Gill Hart is a biochemist and a food intolerance expert at “Yorktest”.

She said the clearest way to tell the difference between a food allergy and an intolerance- symptoms and reaction time.

Allergies are the immediate reaction to food, like swelling of the mouth, diarrhea, or vomiting while food intolerance or sensitivities can take up to two days to appear.

“Those symptoms are very wide-ranging, so you might get anything from IBS, digestive problems, bloating, through to skin symptoms, migraines, headaches, and even low energy and low mood,” she said.

The most common food allergies are to milk, eggs, shellfish, and sesame.

Allergies tend to be developed through childhood or adulthood, and at that point are lifelong.

However, food intolerance can develop at any age and it’s not necessarily permanent.

“We can actually find out from small blood samples, exactly what people are reacting to,” she added.

“Yorktest” is the United Kingdom’s market leader in food sensitivity testing, and has hubs in the United States.

The test identifies up to 200 different foods, in anyone over the age of two.

In a recent study, the company found 80% of the people who took a simple blood test felt better after removing the food identified in the test.

Dr. Hart said after a person removes the problem food from their diet, it’s important to give it two to three months, to get gut health back in check, and then re-introduce it back in, a little bit at a time, to see if there is still a reaction to the food.