1. Open a photo of a person - a fairly close up photo works best for this. Remove any major blemishes with the healing brush tool or however you usually do it. When you're photo is almost ready to save, do this technique.
2. Duplicate the photo layer by clicking on Layer>Duplicate Layer OR just click on the thumbnail of your photo on your layers palette and drag it onto the "create a new layer" icon to the bottom right. What you will see is a duplicate of your image on your layers palette. You can name this layer "Smooth Skin" if you'd like.
3. Now you will add the "Surface Blur" filter which will smooth and kind of blur the entire photo. Don't worry about that - we'll be fixing it soon. So, click at the top of the screen on Filter>Blur>Surface Blur.
You'll see a little screen pop up that looks like this:
Where it says "Radius" enter a number around 15. Set the "Threshold" to around 20. Click OK
4. Now your photo will look smooth ALL OVER. We don't want that, right? We just want the skin to be smooth! And, we definitely don't want it to look PLASTIC, so we are going to add a little bit of "noise" (or grain) to the photo to get rid of the plastic look. Click on Filter>Noise>Add Noise
5. Enter "2", and make sure that "Monochrome" is checked. Click OK.
6. Now you'll have a "smooth skin" layer on top of your background layer. If you click on the little "eyeball" to the left of your "smooth skin" layer on your layers palette, you'll be able to see the difference already. However, this has smoothed and blurred the entire photo, and we just want the skin, so we have to create another duplicate of the background layer by clicking on the background thumbnail on your layers palette. It's the one on the bottom. Then repeat the steps in step 2. Layer>Duplicate layer. Now you'll have another layer called "Background copy" right above your background layer on your layers palette. Drag that copy to the top of your layers palette. So, now your layers will be in this order:
7. Select the eraser tool on your tools palette and set the opacity to 100%. Now, you can erase over the skin on your "background copy" layer and watch as the smooth skin layer magically shows! Be careful to avoid eyes, eyebrows, eyelashes, nostrils, hair etc. JUST do the skin. If the smoothing is too much, then just lower the opacity of the skin smoothing layer in your layers palette until you like how it looks. When you are happy with the results, you can flatten your image!