STS is usually applied via an HVLP (High Volume Low Power) or airbrush system. The solution once applied produces a tan which generally develops over the next 5 - 10 hours. The tan wears off over the next 1-3 weeks.

STS contains dihydroxyacetone (DHA) as the active ingredient. DHA is a colourless chemical (it is derived from sugar cane) that interacts with the amino acids in dead skin cells to produce a brown colour change. Since these dead skin cells are constantly being shed, the colour change produced by DHA usually lasts about five to ten days but there are reports of tans lasting upto four weeks.

DHA is not absorbed through the skin into the body and it has no known toxicity. DHA was first discovered by the Germans in the late 1920's & has been used in cosmetic preparations for almost 30 years.

STS can also contain other ingredients which can affect the quality of the tan & the durability of that tan. Some of these ingredients can include Aloe Vera which will help sustain the tan through skin moiturisation & Eurythrolose which has a similar effect to DHA but because it is very expensive it can be left out of some cheaper STS's.

Many STS's quote the % of DHA which can act as a guide to darkness of the tan they should perhaps quote the Eurythrolose content as well. A good STS is in fact a balance of all the ingredients, simply going for a higher DHA is not always the best way to go. It is for this reason that you should be wary of companies which seem to offer STS in many different % DHA as often they simply add more drops of pure DHA but fail to balance the solution with proprietary ingredients such as Eurythrolose. Generally the higher the DHA content the longer it will take to dry & the tackier it will feel on the skin & the more chance you have of rubbing it off before the DHA has had time to "take", this can produce a patchy affect. More care must be taken when dealing with solution which is a higher DHA. The strongest spray tan (at 15% DHA) is Siennasol Extreme.

STS is usually available in tinted or clear. Most people go for the tinted as it can sometimes be easier to see where you have been, however with a bit of experience & a good application regime clear STS can sometimes be the preferred solution for the more experienced spray tan technician, as it stops the solution staining cloths, walls, carpets etc. Clients love to see their actual tan develop over time. The bronze pigment bares no relation to the final tan & will wash off after their first shower.

Because of these variations it is always a good idea to try a tan before you commit to that five litre bottle. Also ensure that you are buying fresh stock, & if you decant it ensure it is into a suitable HDPE plastic bottles. STS should be stored in a cool dark place (preferably a fridge).

STS may not be suitable for everyone occasionally some people can have an allergic reaction to DHA. There are also certain skin conditions which may result in an uneven, unattractive "tan." These conditions include skin that has been previously damaged by the sun, "older" skin, mottled or freckled skin and scars. Care should also be taken to prevent DHA colouration of the hair and nails. It should also be noted that a sunless "tan" is not really a suntan and affords no protection whatsoever against the skin damage the sun may cause.

It has been known for tans to last upto four weeks, sometimes it can just come down to an individuals skin type however there are steps the client can take before application, which will help the tan to last longer, these can include a full body exfoliation (with particular attention paid to knees & elbows). Exfoliating basically eliminates the already-dead skin cells, which means that the spray tan mist will dye the layer of skin that is likely to last for a longer period of time. Encourage the client to not apply any deodorants, perfumes or makeup prior to application, sometimes shaving prior to application can also help prolong the tan. After application clients should be encouraged not to bath for six hours & to keep their skin well moisturised. It should be noted that the STS will only stain the outer layer of the epidermis therefore anything that could encourage exfoliation of this top layer of skin may shorten the life of the tan. If someone exercises daily & showers three times a day then towels themselves down vigorously then the tan may only last a few days.

I am not going to go into the machines (which you can use to apply spray tan) here but you should take into consideration just how noisy some machines can be & the amount of overspray they can produce (particularly the HVLP systems), also you should consider the after sales service you will receive from the manufacturer. If you are planning to take it up professionally you should also ensure that you receive training from an officially verified & insurable training school. If you are setting up on your own keep records of everything from day one.

Richard is an independent beauty consultant, editor and publisher of www.siennasol.co.uk - spray tan articles and resources online.