Metabolic engineering continues to evolve in efficiency and processes aided by breakthroughs in the field of synthetic biology and progress in understanding metabolite damage and its repair or preemption. Early metabolic engineering experiments showed that accumulation of reactive intermediates can limit flux in engineered pathways and be deleterious to host cells if matching damage control systems are missing or inadequate. Researchers in synthetic biology optimize genetic pathways, which in turn influence cellular metabolic outputs. Recent decreases in cost of synthesized DNA and developments in genetic circuits help to influence the ability of metabolic engineering to produce desired outputs.