The S project was designed as a randomised controlled trial with simultaneous brief interventions.
The study population was randomised to receive messages about either safer sex or sun safety over a 4-month period.
Mobile advertising subscribers aged 16–29 years residing in Victoria, Australia ( = 7606) were randomised to the ‘sex’ or ‘sun’ group and received eight messages during the 2008–2009 summer period.
Mobile phone text messages (SMS) are a promising method of health promotion, but a simple and low cost way to obtain phone numbers is required to reach a wide population.
We conducted a randomised controlled trial with simultaneous brief interventions to (i) evaluate effectiveness of messages related to safer sex and sun safety and (ii) pilot the use of mobile advertising for health promotion.
These behaviours were targeted as young people frequently report exposures (multiple sexual partners, inconsistent condom use, infrequent use of sun protection measures [23, 24]) that place them at risk of significant long-term consequences (infertility as a result of chlamydia infection, melanoma [25, 26]).
At the time of study conception, the only known SMS studies addressing safer sex and sun safety issues were the SEXINFO service in San Francisco  and our own previous SMS studies of sexual health promotion to young people [17, 18]; we could find none related to sun safety.
In this article, we describe a study of the use of SMS for health promotion at a population level.
The S (SMS for safer sex and sun safety) project was designed as a randomised controlled trial with simultaneous brief interventions aiming to improve behaviours around safer sex and sun safety in young people.Mobile advertising (advertising delivered directly to mobile phones) offers a novel way to reach a potentially huge number of individuals.The mobile advertising market is growing rapidly, with an estimated increase in market size of 85% in 2009 alone .All text messages were designed prior to the commencement of the broadcast period.The messages aimed to increase knowledge, reinforce protective behaviours, change attitudes and increase perceived behavioural control.Short message service (SMS)—text messages sent via mobile phones—is a highly promising method of health promotion to young people.