Asked and answered twice already. If one spouse itemizes, that will force the other spouse to itemize.
Here it is in the actual law, 26 USC §63(c)(6)(A)
"In the case of a married individual filing a separate return where either spouse itemizes deductions, the standard deduction shall be zero."
More info & Head of Household info
Many people think they come out better when filing Married Filing Separate but they are probably doing it wrong. If one person itemizes deductions then the other one must itemize too, even if it's less than the standard deduction, even if it is ZERO!
See pub 501 page 7 rule 11, https://www.irs.gov/pub/irs-pdf/p501.pdf
But the rules are a little tricky for Head of Household.
The person filing HOH does not have to itemize unless they want to, BUT the person filing MFS MUST itemize if the HOH Spouse does.
The rule for MFS says you MUST Itemize if your spouse Itemized.
The rule for HOH says you do not have to Itemize if your spouse does.