The fundamental distinction for hair health lies not in the format (solid vs. liquid), but in the chemical composition: 'syndet' (synthetic detergent) bars are balanced to respect the scalp's natural pH, whereas traditional soap bars are often too alkaline, which can damage the cuticle and cause adverse effects.

noli's read

The community is converging toward a clear technical consensus: a distinction must be made between 'syndet bars' and 'saponified soaps.' Evidence from cosmetic formulation (expert/formulator opinions) confirms that pH is a determining factor for the integrity of the hair cuticle (around 4.5-5.5). The claim that solid shampoos are inherently more aggressive is considered exaggerated; it often stems from the use of basic soaps (pH 9-10) that leave residues or cause a rough sensation in the hair. Conversely, bars using synthetic cleaning agents (e.g., SCI) share the same basic chemistry as quality liquid shampoos and do not cause more issues with dandruff or residues. Observational research via user feedback suggests that an adaptation period may be necessary, related more to application technique than to any biological transformation of the scalp.

the sources

1. 1r/HaircareScience