Hydroxide relaxers versus thio relaxers

One distinction generates more exam items than any other in this domain, and it also generates the most real-world breakage: the two relaxer chemistries are incompatible, in both directions, permanently.

Hydroxide relaxers	Convert disulfide bonds into lanthionine bonds — lanthionization, irreversible
Thio relaxers	Break disulfide bonds; an oxidizing neutralizer rebuilds them in the new shape
The lye relaxer	Sodium hydroxide
The no-lye relaxers	Potassium, lithium and guanidine hydroxide — still hydroxide, still lanthionization
A guanidine relaxer	Calcium hydroxide cream plus a guanidine carbonate activator, mixed on site
After a hydroxide relaxer	An acid-balanced neutralizing shampoo — it restores pH; it rebuilds nothing
pH	Strongly alkaline, above 11
Base cream	An oil barrier on scalp, hairline and ears — not on the hair itself
Virgin application	Start a quarter to half an inch off the scalp; that zone is done last
Choosing mild, regular or super	By texture, porosity and resistance — never by how straight she wants it

Where the point is lost: Time does not repair an incompatibility. Hair relaxed with hydroxide eight months ago still cannot take a thio wave, because the lanthionine bonds are not coming back, and hair relaxed with thio six months ago still must not receive hydroxide. Only new growth is ever treatable. The same caution covers recently lightened hair: bonds are already broken and porosity is already raised, so a release form documents consent without making the service safe.