Everyone has candida because it is a normal component of gut flora. It is only a problem if it takes over and crowds out the good bacteria (it is those bacteria that help digest your food and which make most of your vitamin K which keeps your blood clotting normally when you are cut). Candida can also go into a growth phase where it actually invades the mucosal lining and cause gastric upset and leaky gut. This can lead to other food allergies as more foods come into contact with the cellular parts of your immune system. Some people, like me, actually have an allergy to candida cytoplasmic proteins which makes it all the more important to keep the yeast levels low.

My doctor said that anyone who has taken lots of antibiotics (for example I took tetracycline for complexion for about 6 months), eats lots of sugar and has digestive symptoms, fatique disorders or chemical sensitivity is at risk for yeast overgrowth.

If you get whitish lesions in your mouth (thrush) or lots of vaginal yeast infections, those are another obvious sign.

I've heard of fecal testing but honestly don't know what they are testing for other than dead yeast but everyone should have some. I guess they must look for the numbers of yeast proteins or something to tell if you have too many or not.

Serious yeast overgrowth can occur when someone is immuno-compromised since our immune systems normally keep the yeasties in check and out of mucosal linings in their invasive growth phase.

I think yeast are a symptom of a gut that is in poor shape rather than the cause of the poor shape but I may be in the minority on that opinion.