What are substances added to conditioners to help hair retain moisture called?

Humectants are substances incorporated into conditioners specifically designed to help hair retain moisture. They work by attracting water molecules from the environment into the hair, which results in improved hydration and moisture retention. This is particularly beneficial for preventing dryness and maintaining the health and elasticity of hair, making it appear smoother and more manageable.

Emollients, while also beneficial for hair, mainly serve to soften and smooth the hair's surface rather than actively attracting moisture. Surfactants focus on cleansing and emulsifying, helping to lift dirt and oils from hair and scalp but do not contribute to moisture retention. Conditioners as a whole may contain a mix of ingredients, but humectants stand out for their moisture-retaining properties specifically, which is why this is the correct answer in the context of the question.