In Wolverhampton, it was discovered that underage people were being sold Botox and other fillers illegally.
Trading Standards discovered that eight out of the sixteen businesses it contacted during its operation stated they did not require ID for a consultation.
Even with parental consent, injecting Botox or another cosmetic filler into a person under the age of 18 is illegal.
The City of Wolverhampton Council reported that written warnings had been given.
Advice letters outlining the law and cautioning against potential test purchases had been sent to companies identified as possibly providing Botox or fillers.
A supervised 15-year-old volunteer made test calls after receiving the letters, and three of the eight businesses said they would schedule a consultation appointment even though they were aware the caller was under 18.
Eight others stipulated that the person calling must be over 18 and required them to bring identification with them to the consultation.
Trading standards officials had "uncovered some shocking results," the council claimed.
Businesses "must bring their practices into compliance with statutory requirements or face prosecution, which may result in them receiving a significant fine," it warned.
