Note on Brands: Different types of deodorants within a brand contain different ingredients. Listed below are brands when at least one type of its deodorant has the ingredient - check your ingredient list for confirmation.
1. Aluminum Chlorohydrate, Aluminum Zirconium Tetrachlorohydrex Gly, other Aluminum Compounds
- Prevents sweat via cell swelling which squeezes the sweat ducts closed
- People with skin sensitivities can develop a rash from this ingredient.
- People with Alzheimer's Disease have higher levels of aluminum in their brain than is usual. I have found no evidence that conclusively states whether this is a cause or effect of the disease - I don't think we know yet. While prolonged use of deodorants with this ingredient can cause the accumulation of Aluminum in the body, there is no scientific evidence that I've found indicating that this is a direct cause of Alzheimer's.
Deodorants with Alumnium compounds: Sure, Right Guard, Secret, Gillette, Almay, Arrid, Ban, Mitchum, Speed Stick by Mennen, Dry Idea, Degree
2. Parabens (methyl, ethyl, propyl, benzyl, buytl)
Note: Parabens can also be found in plant extracts and do not have to be listed on the label - call the manufacturer for deatiled information.
- Can cause skin irritation and contact dermatitis
- 20 samples of malignant breast cancer tumors show paraben content in a 2004 Journal of Applied Toxicology report, but no control was done in this study on paraben content in healthy breast tissue
- Parabens injected into animals have shown tumor growth stimulating properties
- No scientific evidence indicating low paraben dose in deodorants and other cosmetics as a health risk at this time
- Overuse could cause antibiotic-resistant strains to emerge but in 30 years of use, no such reistances have been reported
- FDA classifies as a pesticide
- Tricoslan mixed with the chlorine found in tap water can produce chloroform gas - an EPA classified human carcinogen (cancer-causing agent)
- The chemical reaction mentioned above can also produce dioxins when exposed to sunlight and other UV sources, which are extremely toxic and can disrupt proper endocrine system function
Deodorants with Tricoslan: Old Spice
- Powder material (is that all? It'll all I could surmise)
- Classified carcinogen by the International Agency for Research on Cancer due to presence of asbestiform fibers
- % of asbestiform fibers per Talc ingredient is unregulated, so an ingredients list with Talc could have only trace elements or be mostly asbestiform and there would be no way to know
- Preliminary research suggests that talc may be associated with pulmonary issues, lung cancer and ovarian cancer
- The FDA endorses only non-abestiform talc to be Generally Recognized As Safe (GRAS)
Deodorants with Talc: Arrid, Arm & Hammer, Degree
5. Propylene Glycol
Note: Propylene Glycol can also be found in plant extracts and do not have to be listed on the label - call the manufacturer for deatiled information.
- FDA classifies as Generally Recognized As Safe (GRAS)
- Body naturally metabolizes propylene glycol into lactic acid (naturally occuring acid when muscles are exercised)
- National Institute for Occupational Safety and Health (NIOSH) classifies propylene glycol as a neurotoxin which may cause kidney or liver damage
Deodorants with Propylene Glycol: Old Spice, Tom's of Maine, Trader Joe's, Right Guard, Gillette, Dry Idea, Arm & Hammer
- Absorbs water
- Skin irritant
- Can be contaminated with crystalline quartz, and the inhalation of crystalline silica can lead to silicosis (respiratory disease) or cancer
Deodorants with Silica: Old Spice
7. Steareth-n (where n is a number)
- "may be vegetable derived but is reacted with ethylene oxide (ethoxylated), a known human carcingoen" 
Deodorants with Steareth-n: Trader Joe's
8. Artificial Colors
Most artificial colors are derived from coal tars which are known carcinogens.
I haven't found evidence that any of the dyes/colors from this list are found in deodorants, but if you're curious to read more about the health effects of dyes and artificial colors not listed here, it's a good place to get started.
a. D&C Violet No. 2 (Old Spice)
- FDA ban on food
- FDA ban on eye cosmetics
- Cosmetics Ingredient Review board has not assessed for safety
b. D&C Green No. 6 (Old Spice)
- Info N/A
5. http://www.drugstore.com - Ingredient Lists