Solid shampoo is gaining attention as a potential solution for reducing environmental impact in the cosmetics industry, but its adoption faces both technical and behavioral challenges. Since the 1930s, liquid shampoo has shaped expectations of foam, detangling, and softness, making the transition to solid formats complex. Formulating a high-performance solid shampoo is a real technical challenge, requiring a complete reformulation rather than simply concentrating an existing liquid recipe. The process involves replacing ingredients that are unsuitable for solid formats, as some surfactants are only available in liquid form or contain significant amounts of water, which limits their incorporation into solid formulations. Solid shampoo is not a return to soap, which has limitations for hair care due to its alkaline nature. Instead, many solid shampoos use synthetic surfactants, or syndets, which are better suited to hair and scalp. These surfactants can be derived from renewable raw materials such as fats, sugars, or amino acids. However, the challenge lies in maintaining the performance of modern shampoos while adapting to the physical properties required for a solid format. Issues such as the hardness and plasticity of the bar, its cracking, softening, loss of mass during use, and the quality of the foam obtained must be addressed. The movement toward solid cosmetics, including shampoos, has been rapid, with the French market for solid cosmetics growing from 1% to 7.5% of consumers purchasing at least one product between 2019 and 2021. However, the market has since receded by 3.2% in volume in 2022 and 2023, indicating that initial enthusiasm does not necessarily lead to the durable establishment of new practices. This decline may be attributed to factors beyond the sensory characteristics of the product, such as price, distribution, economic context, or evolution of the product offering. Adopting solid shampoo sustainably may require rethinking expectations from shampoo. Consumers may wish to reduce packaging and water usage while continuing to seek the sensory qualities they have grown accustomed to. The transition to solid shampoo could therefore involve not only product innovation but also a shift in consumer behavior and expectations.