What is the difference between docosahexaenoate (DHA) and 19,20-dihydroxydocosapentaenoate (19,20-DHDP)? Only DHA is a polyunsaturated fatty acid. DHA has a higher melting point than 19,20-DHDP. 19,20-DHDP is more polar than DHA. Only DHA is a an ω ω -3 fatty acid.