Citra Formaldehyde Free helps to develop stronger, flexible nails in a safer, more natural way. Safe and effective proven to strengthen nails. Naturally occuring aldehydes derived from citrus sources completely replace formaldehyde. These natural elements provide the strengthening characteristics of aldehydes with the helath and safety of pure citrus. How to Use Clean and prep nails. TREAT with one coat of Citra 3 as a base coat.