What is DHA?

In short DHA is the chemical in self tanners which makes you go dark.

Dihydroxyacetone is primarily derived from sugar cane & is a white powder with a very distinctive almost sickly sweet smell. It was initially used as an oral medicine (in the 1950's), where it was found that it would dye the skin when spilt.
Generally speaking the higher the percentage of DHA the darker the tan (should) go.

Until recently the tan with the highest DHA content was Siennasol Extreme (which is 16% DHA), but recently several manufacturers have upped the DHA to as high as 20%, but this isn't the whole story. Skin can only go so dark with DHA alone so we begin to get diminishing returns. The difference between a 10% & a 14% is significant, however going from a 16% to a 20% is not that noticeable. Skin can begin to become sensitive to higher percentages of DHA & although the FDA have passed DHA as being safe for external use, some manufactures are resistant to pushing the DHA levels much beyond 16%.

Perhaps a safer & more sensible way to increase the depth of a spray tan is to include Erythrulose in the tan. Erythrulose is very similar to DHA, but takes a little longer to develop & actually makes the tan last longer. The picture on the left shows how after being left for a few day, the tan containing the Erythrulose lasts longer.

As a spray tanning ingredient it is very expensive so some manufacturers won't include it in their spray tan even though it invariably produces better results.

What has been happening recently in spray tanning is a constant push to increase the DHA content of spray tan, pushing it ever higher. This is lead by a demand by consumers for an ever darker tan.

Unfortunately Throwing more DHA, into a mix will not necessarily make it darker, it will however increase the chances of getting a reaction. Although DHA has been tested & deemed safe it has not been tested at such high levels.