The answer to this question is both simple and a tad complicated. Leather is a natural material made from animal skin. So, it will react to the sun in much the same way that your skin would. If you spend too much time in the sun your skin will darken, dry out and crack and just not be very healthy. Leather will also become discolored, dry out and crack if left out in the sun. It will prematurely age your leather and affect its softness and strength.
The reason why all of these changes occur in your leather is because of the sun’s ultraviolet rays. The first thing these rays will do to leather after prolonged exposure is change the color of the leather. This in and of it itself isn’t a problem. Your leather is going to change color as it ages and through regular use. Many people actually like when their leather changes color and gets that aged look.
Can Leather Be Left Out in the Sun?
The problem is that this color change from the sun means that other changes are happening to the leather on the molecular level. Leather is a porous material; you’ll find that it absorbs moisture easily if you get caught in the rain. Unfortunately, this also means that it can lose moisture easily. The UV rays will drain the moisture from the leather leaving it very dry and brittle. The leather may also lose many of its natural oils and these cannot be replenished.
This does not mean that your leather bags should never see sunlight. You can let them out in the sun as much as you are but they never should be left out in the sun for an extended period. Also, you can help prevent sun damage to your leather goods by conditioning them regularly.