Note: This advice is given by the CAP Executive about non-broadcast advertising. It does not constitute legal advice. It does not bind CAP, CAP advisory panels or the Advertising Standards Authority.


Before submitting marketing communications for publication, marketers must ensure that they hold documentary evidence to prove all claims, whether direct or implied, that are capable of objective substantiation (rule 3.7).

How do I know if my claim requires substantiation?
What about comparative claims?
Don’t rely on testimonials alone
Take particular care when referring to health and beauty products
Are there any exceptions?

How do I know if my claim requires substantiation?

If a claim is capable of objective substantiation, the marketer will be required to hold adequate supporting evidence. Marketers should be mindful of the fact that if the ASA considers a claim to be objective and capable of substantiation, they are likely to rule the claim misleading in the absence of adequate substantiation, even if the marketer’s intention was to make a subjective claim. See Types of Claims: Subjective or Objective Superlative for more guidance on how to distinguish between objective and subjective claims.

What about comparative claims?

Marketers wanting to make objective comparative claims, such as “leading”, “best”, or “cheaper”, for example, must hold evidence relating to both their own products and those of the competitor or competitors that are the subject of the comparison. Comparative claims can be both implicit and explicit and relate to both identifiable and non-identifiable competitors.

In April 2016, the ASA ruled against a claim that a facial cleansing product was the “UK’s most effective anti-bacterial face wash”, because while the marketer submitted evidence to support the claim, not only had the testing concerned only been carried out on leading competitors, rather than the whole market, they concluded that the evidence did not prove there would be a perceptible difference in effectiveness for users of the product (Medichem International (Manufacturing) Ltd, 13 April 2016). See Comparisons: General, Comparisons: Verifiability and "Types of Claims" entries.

Don’t rely on testimonials alone

Provided they are genuine, marketers may feature customer testimonials in their advertising, but these alone are unlikely to be considered sufficient to substantiate objective claims. Where they are likely to be interpreted as objective claims, the opinions expressed in testimonials must be supported by independent evidence of their accuracy (rules 3.45, 3.46, and 3.47). In February 2015, an advertiser submitted testimonials in support of efficacy claims for a copper bracelet in the treatment of restless leg syndrome and the ASA ruled that personal or customer endorsement alone did not constitute adequate substantiation (Halcyon Bracelets, 18 February 2015). See Testimonials and endorsements and Claims in testimonials and endorsements.

Take particular care when referring to health and beauty products

Medical and scientific claims made about health and beauty products, including weight control products, food supplements and cosmetics, should be backed by evidence, where relevant consisting of trials conducted on human subjects (see rule 12.1 (health and beauty products and therapies), 15.7 (vitamins, minerals and other food supplements), 12.22 (cosmetics), 12.23 (hair and scalp) and 13.1 (slimming)).

Marketers of health and beauty products wanting to make breakthrough claims about a product or treatment will need to hold a high level of robust evidence and should collate sound data to form a body of evidence. That body of evidence will usually need to include properly controlled human experimental studies. See Substantiation for health, beauty and slimming claims and CAP’s Advertising Guidance on this topic, for detailed guidance on the type of evidence the ASA is likely to expect marketers to hold.

Are there any exceptions?

While claims capable of objective substantiation will, generally, require supporting evidence, obvious untruths or exaggerations (“puffery”), which are unlikely to be taken literally by the average consumer are likely to be considered acceptable, provided they do not mislead consumers materially (rule 3.2). In 2013, the ASA ruled that the claims "to achieve the unachievable" and "Comfort redefined" in trade magazine ads for a contact lens brand would be understood as puffery, rather than objective claims based on evidence (Alcon Eye Care UK Ltd, 4 September 2013).

Claims which are obviously a marketer’s subjective opinion and are unlikely to be interpreted as objective claims will not usually require supporting evidence, provided it is clear that marketers are expressing their opinion, rather than stating a fact (rule 3.6). In 2014, for example, the ASA considered whether the claim "The most comfortable beds in the world", in an ad for Hypnos beds, was misleading and could be substantiated and they agreed with the advertiser’s view that the claim was subjective, given the experienced comfort of mattress types would vary between consumers (Hypnos Ltd, 26 November 2014). See Matters of opinion.

See Misleading Advertising

Updated 9 June 2016


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