My naturopath first told me this. Vitamin D can take upto 48 hours to be absorbed through the skin upon first exposure to sunshine...using soap and water on the skin can interfere with the chemical reaction says Dr. Mercola... http://articles.mercola.com/sites/a...-actually-decrease-your-vitamin-d-levels.aspx quote:" But first, I want to review something that’s even more surprising – the connection between exposure to sunshine, vitamin D3, and showering! What Does Showering Have to Do With Your Vitamin D Levels? First, it’s important to understand that vitamin D3 is an oil soluble steroid hormone. It’s formed when your skin is exposed to ultraviolet B (UVB) radiation from the sun (or a safe tanning bed). When UVB strikes the surface of your skin, your skin converts a cholesterol derivative in your skin into vitamin D3. However, the vitamin D3 that is formed is on the surface of your skin does not immediately penetrate into your bloodstream. It actually needs to be absorbed from the surface of your skin into your bloodstream. The critical question then is: how long does it take the vitamin D3 to penetrate your skin and reach your bloodstream? If you’re thinking about an hour or two, like I did until recently, you’re wrong. Because new evidence shows it takes up to48 hours before you absorb the majority of the vitamin D that was generated by exposing your skin to the sun! Therefore, if you shower with soap, you will simply wash away much of the vitamin D3 your skin generated, and decrease the benefits of your sun exposure. So to optimize your vitamin D level, you need to delay washing your body with soap for about two full days after sun exposure. Now not many people are not going to bathe for two full days. However you really only need to use soap underneath your arms and your groin area. , so this is not a major hygiene issue. You’ll just want to avoid soaping up the larger areas of your body that were exposed to the sun. Research Yet to Be Published I realize that the bulk of the"conventional" thinking on how vitamin D is formed in the skin does notsupport what I am telling you. Most of this research is based on Dr.Michael Hollick's work. However that is over 25 years old and there isnew evidence that suggests the currently described on vitamin is formedis not accurate. Dr. Cannell will actually be publishing a paper specifically detailing this position later this year. Rest assured as soon as the paper is published I will let you know about it. But in the meantime the logic behind this position is really quite solid. As of this date no one has ever tested whether vitamin D is formed in human sebum, the fat that your skin produces. The only study that support that vitamin D3 is formed in the dermal epidermal junction was done in humans were the sebum was removed from the skin. However, this has been extensively tested in animals and that is precisely where the vitamin D3 is formed. In fact that is where most of the oral vitamin D3 in supplements comes from, lanolin and the sebum like material in the skin of sheep and cows Additionally you can rub vitamin D3 on your skin and it easily penetrates into your bloodstream (assuming you don't wash it off for 48 hours). This is also likely the reason why surfers in Hawaii who are in the sun and water continuously don't have vitamin D levels comparable to lifeguards that don't go in the water. The surfers typically have levels in the 70s while the lifeguards and other who are in the sun as much without going into the water will have vitamin D levels around 100. The bottom line is that washing the sebum off of your skin is NOT good and should be avoided. You were NOT designed to use soap. It is fine to wash areas that are prone to bacterial overgrowth such as your axilla (armpits) and groin but it is in your best interest to leave the sebum that was designed to be on your skin, to stay on your skin. Obviously you can do as you wish, but it is my STRONG recommendation to avoid soap on most of your skin."