Any change in the nail plate is a cause for concern - especialy if the nail plate is turning a yellowish color and becomming thicker. This is a classic symptom of some sort of fungal infection - including the ridging. When the nails become thicker, it is because the fungal spores are invading the spaces between the nail plate cells and the space between the nail plate and the nail bed. I would seek the advice of a dermatologist to prevent even further damage from occuring.