Custom and Lookalike Audiences
Custom audiences are target groups for social media advertising built from a company's own data, such as customer lists, website visits or interactions with a profile. Lookalike audiences are derived groups of people whom the platform considers similar to that source data.
In practice
Uploading customer lists is demanding in data protection terms: you need a sound legal basis under the General Data Protection Regulation, must inform the individuals concerned and must pseudonymise the data before transfer as the provider requires. Meta's documentation expressly requires SHA256 hashing and permits no other method (as at August 2026); hashing is a one-way function and not encryption. Check beforehand whether your privacy notice even covers this processing. For small companies, custom audiences built from website visits or profile interactions are usually easier to handle than customer lists. Lookalike audiences tend to deliver usable results only when the source list is large and internally consistent. Audiences built on specially protected data such as health, religion or political opinion are excluded from advertising under the Digital Services Act.