Let's begin with the life span of a foundation. If your foundation has a pump then it will stay fresh longer, but if you are dabbing your fingers into a bottle everyday you should think of tossing your foundation makeup every 6-8 months. If you are prone to breakouts and are using the dabbing method, you should toss you makeup no later than 6 months. If you are using a pump foundation, it should be good for at least 8 months. But keep in mind that your foundation color can change at least twice a year anyway, so just get in the habit of tossing you foundation makeup every 6 months.
Powder face makeup can last over a year, if there is no shiny build up on the surface and you have not had any major skin irritations during use. Honestly though, most people won't be able to make a face powder last for over a year anyway. And as a general rule of thumb, if it smells funny or looks strange you should toss it. Powder blush and powder bronzers also fall into the 1 year category.
Next, let's cover our eyes. Most experts suggest throwing away liquid eyeliner and mascara every 3 months. Personally, I keep my liquid eyeliner and mascara for at least 6 months and then open a new one. Basically if you mascara isn't dry, clumpy, or smells foul then you should be okay for 6 months. The only exception is if you get an eye infection; eye infections mean that you need to toss all eye makeup and start over again. And as for pencil eyeliner, it can last up to 1-2 years, if properly stored and sharpened regularly.
Finally let's cover the lips and nails. Nail polish is a pretty sturdy product and can last up to 2 years, unless you wear it with a fungal infection. Anytime your makeup items come into contact with an infection, they should be tossed immediately. As for lipstick, lip gloss, and lip liner; they can last for up to 2 years, if you don't use them up first.
So in the end, use common sense and if it smells funny or looks strange it should be tossed out. As a general rule of thumb, change out your makeup every 6 months, since your skin will normally change shades during that time. And if there is ever a doubt about whether to keep it or toss it, you should always just throw it out. Plus, by regularly cleaning and maintaining your makeup items, they will last you longer and keep you healthier as well. And finally, if you have switched to natural makeup make sure you give the products a regular smell check, since they could turn rancid quicker because of the lack of preservatives.
