Alkali-activated aluminosilicate materials, known as "geopolymer", have been extensively investigated in the past 40 years and have been developed from laboratory mock ups to real structural usage in construction in the last decade.While numerous life cycle analysis and carbon accounting studies show the "green potential" of this material compared to Portland cement, some authors state that the high alkali concentration in geopolymer is a potentially unstable factor which may lead to, for example, efflorescence.This paper presents a review of literature and some new experimental work regarding the possibility of efflorescence in geopolymer products.Subjects of the discussion include: (1) the role of alkalis in geopolymers, (2) the effect of alkali concentration on efflorescence, (3) the effect of solid precursor selection on efflorescence, (4) the effect of curing scheme and chemical additives on efflorescence, and (5) the impacts of efflorescence on the microstructural properties of geopolymers.Particular attention is given to the relationship between pore structure and efflorescence behavior,and consequently the mechanical properties of geopolymers suffering from either efflorescence or alkali loss (by leaching).The changes in sodium aluminosilicate hydrate (N-A-S-H) gels due to efflorescence or alkali loss are critical to the durability of geopolymers.This paper highlights that the nature of the solid precursor and the pore structure of the resulting geopolymers are the two most important factors that control efflorescence rate.However, considering the alkaline nature of geopolymer, it seems difficult or impossible to avoid this issue,although kinetically controlled diffusion of alkalis using phase transformation techniques may help to mitigate efflorescence.Efflorescence in geopolymer is a "skin issue" that needs to be carefully treated.It is recognized to be different from the visually similar, but chemically distinct, efflorescence that occurs in Portland cement based materials.