Indigo is one of the most widely used dyes for textiles and is thus produced in large quantities. Owing to its low solubility, a chemical-dependent continuous reduction-oxidation process is often used for indigo dyeing. Unfortunately, the indigo dyeing process has adopted a hazardous reducing agent such as Na₂S₂O₄, to reduce indigo into leucoindigo, thus causing serious water pollution in the process. To avoid this, the use of chemical reducing reagents was banned, creating a need to identify alternative reducing agents or to develop more eco-friendly dyeing processes. In this review, alternative reducing reagents such as biochemicals, plant fruits, biocatalysts, and microbes, which are less harmful to the environment than chemical reducing reagents, are summarized with their reducing reactions and performance. In addition, alternative modifications of indigo that bypass the use of reducing reagents have also been briefly introduced. The reducing chemicals and processes summarized have their respective merits and drawbacks; however, further research is required to obtain profitable dyeing performance that meets economic goals.

靛蓝是最广泛使用的纺织品染料之一，因此大量生产。由于其低溶解度，依赖于化学的连续还原-氧化工艺通常用于靛蓝染色。不幸的是，靛蓝染色工艺采用了危险的还原剂，例如 Na ₂ S ₂ O ₄，将靛蓝还原成无色靛蓝，从而在加工过程中造成严重的水污染。为避免这种情况，化学还原剂的使用被禁止，因此需要寻找替代还原剂或开发更环保的染色工艺。在这篇综述中，对环境危害小于化学还原剂的生化剂、植物果实、生物催化剂和微生物等替代还原剂的还原反应和性能进行了总结。此外，还简要介绍了绕过使用还原剂的靛蓝替代修饰。总结的还原剂和工艺各有优缺点；然而，需要进一步研究以获得符合经济目标的有利可图的染色性能。