As a chemist would explain, the iodine index measures the potential of oils going rancid when used on baseball gloves. Included is information about potential health effects and list some common oils used on baseball gloves along with their associated iodine index values.

When oils are exposed to oxygen in the air, they can undergo a process of oxidation. Oxidation can be accelerated by factors such as heat and light — think warm sunny day.  Oxidation leads to the formation of highly reactive free radicals, which can damage the oil and cause it to go rancid. Rancidity refers to the development of off-flavors, odors, and the degradation of the oil's nutritional value to the point that it can make a person feel ill. 

Technically, the iodine index is a measure of the degree of unsaturation in a fatty acid or oil. Unsaturated fatty acids contain double bonds in their carbon chains, which make them more prone to oxidation. The iodine index quantifies the number of double bonds present in the fatty acids or oil.

In the context of baseball gloves, oils are used to condition and preserve the leather. The natural oils in the leather can gradually dry out and deteriorate over time, leading to stiffness and cracking. Conditioning oils are applied to replenish the lost moisture and maintain the flexibility and durability of the leather. However, if the oil used has a high iodine index, it indicates a higher level of unsaturation and greater susceptibility to oxidation/rancidity.

When an oil with a high iodine index is applied to a baseball glove, it can oxidize more readily upon exposure to air and sunlight as happens throughout the baseball season. This oxidation process can lead to the formation of undesirable compounds, including aldehydes, ketones, and peroxides, which contribute to the rancid odor and health concerns. The glove may become sticky, greasy, or develop a foul smell, making it less pleasant to use.

Moreover, from a health perspective, rancid oils can have adverse effects. Consuming rancid oils can cause gastrointestinal discomfort, including nausea, diarrhea, and vomiting. Inhaling the unpleasant odors from rancid oils may also cause respiratory irritation and discomfort.  The greatest concern is with children.  If you watch a child with a glove in their hand during slow times of a game, they often put the glove to their mouth.  If the oils used to condition the glove have gone rancid, it could make the child sick.

Here are some commonly used oils on baseball gloves, along with their associated iodine index values:

1. Neatsfoot Oil: Iodine Index around 84-88

2. Mink Oil: Iodine Index around 87-91

3. Lanolin Oil: Iodine Index around 88-92

4. Coconut Oil: Iodine Index around 10-20

5. Olive Oil: Iodine Index around 75-94

6. Almond Oil: Iodine Index around 93-105

7. Mitt-Spit Glove Oil: Iodine Index of around <1-1

Clearly, the safest Glove Oil is the one with the lowest Iodine Index - Mitt-Spit Glove Oil. It's important to note that these values may vary slightly depending on the specific brand or source of the oil. Choosing an oil with a lower iodine index generally indicates a lower susceptibility to oxidation and a reduced risk of rancidity.

When selecting oils for conditioning baseball gloves, it's recommended to opt for oils with lower iodine index values to minimize the chances of rancidity and ensure the longevity of the glove's leather.