Yellowing of nails on the fingers or toes often have different causes.

Fingernails stay healthiest when they are not covered with polishes, artificial nails, and glues for too long. Exposure to air and lots of water are what keep nails healthiest, and frequent application of nail conditioner or simple hand cream help as well.

This doesn't mean not being able to wear nail polish all the time. It does mean changing it frequently, and also giving nails the occasional day or two to "rest" once in a while. Washing nail polish remover off well and immediately is an important first step after removing old polish, as well. Acetone remover is more drying, so even if you don't use artificial nails or tips, it's wise to stay away from remover with acetone in it.

When nail polish (or artificial nails) has been left on for more than two or three days, when it is removed the nails will appear dramatically drier and less naturally "pink". The healthier color starts to return after that first good washing-off of the remover, but it can take a little while if the nails that have been covered with old polish for too long.

Although it isn't necessary to NEVER immediately polish nails after removing old polish, giving nails that "rest" between polishings is the best practice. That can be accomplished easily and effortlessly by simply doing something like removing polish in early evening but not putting on a new coat until bedtime; or removing polish before bedtime and applying new polish the next day. When nails begins to appear just slightly less pink and healthy than they ordinarily do, it's a good idea to leave polish off for two or three days; and just go with buffed and conditioned nails for a little while.

The exposure to lots of soap and water (from frequent hand washing, or even from washing dishes) may not do much for the skin on your hands, but it does wonders for nails. With regard to exposure to air, the only real way to accomplish that is to allow time for it. So, how long you treat your nails to fresh air can depend on seriously "troubled" they appear (and feel).

The longer nails are, the older they are; so longer nails are often more prone to losing their glow (and whiteness) than shorter ones are. It isn't always necessary to cut long nails down to "stubs", but giving them a substantial trimming (maybe "half-way down to short") will leave less old nail to "detract" from the healthier appearance of newer part of the nails.

Nails on toes can become yellow for the same reasons that those on fingers do; but toenail fungus is another cause of yellowed (and thickened) nails. Toenails (polished or not) are exposed to drying elements and general abuse when you wear open-toed shoes, but when they're "suffocating" under socks, nylons, and/or shoes of various materials, they aren't in the healthiest environment either.

Toenail fungus needs to be treated with medication specifically designed for that purpose. There are over-the-counter products, but there are also medications that can be prescribed by a doctor. Besides using a medication, it's always a good idea to change your "shoe habits".

Even without toenail fungus, as with fingernails, older nails are more prone to damage and "aging". Toenails that aren't kept very short are prone to being "beaten up" with just the movements of the feet within shoes and normal walking. Keeping toenails softer by using bath oils or moisturizers can help protect them against them against some of the damage to which more brittle nails may be prone.

Whether fingernails or toenails, when nails become damaged they sometimes begin to pull away from the nail bed a little, which essentially means they've been become detached; and no nail that has become detached from the source of growth remains healthy. Pop-top cans are one of the biggest causes of nails that begin to separate; and it's easy to damage a nail, even if you try not to use them while opening pop-top cans. Using something other than your fingertips to open these enemies of nails is always the best idea.

It is important that I make clear that I am not particularly recommending this, but I have discovered that after cleaning something with a paper towel and Comet cleanser (which has bleach in it), my nails are particularly white and healthy looking. Comet cleanser comes in "abrasive" and "non-abrasive", and it happens that buy the "abrasive" version. I suspect that combination of bleach and abrasiveness (which both removes hard-to-remove polish residue and bleaches out any stains) is what makes a product like Comet cleanser whiten nails the way it does.

Completely aware of the fact that it is not a good idea to get too much of this kind of product on the skin around/under the nails, or into open scratches/cuts, there have been times when (after I've left polish a little longer than is good) I've shaken just the tiniest amount of Comet cleanser directly on my fingernails and cleansed them ever-so-gently with a soft paper towel and hot water. It isn't something I've needed to do more than once every couple of years; so, for me, I can't help but think the biggest risk involves not rubbing the cleanser into the skin around/under the nails.

Again, this is not a recommendation. There is the possibility that this is an extremely bad thing to do. Still, my reasoning for myself has always been that the chemicals in cleanser are probably no worse than those in the products we routinely put on our nails. (Let's face it, most of us don't wear gloves when we're cleaning the lawn chairs or the bottoms of pots.) In any case, it works for me. I would be careful to recommend that anyone considering trying this look more into the possible hazards of it.