What can be the cause of yellow arm pits? it almost looks as if its bruised. i am in good health at the moment

Armpits: Get yourself checked for a fungal infection. Another possibility is acanthosis nigricans - a prediabetic condition.

Not sure: I recommend getting the area looked at. At times, the type of deodorant you use can actually stain a persons skin over time from a type of contact dermatitis. Best to get evaluated and have the area seen by a dr. Though to get a definitive dx, best wishes.