Turn on the TV any day in Ireland and you’ll see George Hook flogging SKY, Brian O’Driscoll shaving with Gillette and Brendan O’Connor shopping in Mace. It probably comes as no surprise that one if five adverts across the world feature a celebrity endorsement.

When a celebrity appears in an advert, we perceive the product to be more authentic – and this has a huge impact on our recall and brand recognition.

If the endorser and brand are a good match, the results can be astronomical. After Nike signed up Tiger Woods on a $40 million contract in the mid 90s, sales of Nike golf apparel and footwear doubled soon afterwards. In the UK, the choice of Jamie Oliver as a brand ambassador for Sainsburys helped the grocery chain to gain market share over other supermarket rivals.

For the last few years, Ronan O’Gara has appeared in adverts for the energy drink Lucozade. In the latest series, Ronan talks about the last 15 minutes of the game. By using Lucozade, he explains to the audience how he can keep up his performance. In this example, the choice of O’Gara is a good match for the brand and has allowed Lucozade to maintain its number one spot in the sports drink market.

So why are celebrity endorsements so successful?

Simply, it is down to a psychological phenomenon called transference. This is where we subconsciously transplant our feelings about a celebrity onto a product. For example, if we drink Lucozade ourselves we feel much closer to Ronan and his sporting successes. When we carry around a bottle of Lucozade, we adopt Ronan’s talent, strength and hard work mentality. In many ways, we embody everything that Ronan is and stands for when we consume his favourite sports drink.

Without a credible link between the endorser and the brand, the consumer will only remember the celebrity. In the US, American Express dropped Tiger Woods from their advertisements after he had a minimal impact on their sales. Consumers did not see Tiger as a credible spokesperson for a financial product. Donald Trump would have been a better fit.

It is expected that marketers will embrace celebrity endorsement campaigns further in the coming years. However, there are many issues that need to be considered before celebrities sign the dotted line such as potential bad behaviour, overexposure and the endorser’s use of competitive brands.