In many occupations including professional singer, a clear and healthy voice is a necessary tool to do one's job.  When the voice is not in the best of health, others can tell, and it may negatively affect your performance.  If you understand how your voice works, what can go wrong with it, and how to care for it, it can potentially save your career.

The sound of voice is produced when you exhale while your vocal folds are brought together.  The moving air causes the vocal folds to vibrate.  The vibrating air is bounced around and amplified within the throat, oral and nasal cavities and exits through the mouth. 

Many factors influence how your voice sounds and how well it works.  If your vocal folds are stretched long and tight, you will have a high pitch.  If they are squished short and fat, the pitch will be low.  Depending on how you set your palate, mouth opening, and tongue, your nasality and vowel quality will be different.  If you involve muscles not strictly necessary for singing or speaking, your tone will have a tense muscular sound and you will fatigue much more quickly. 

• When you force a lot of air between your folds for a long time (such as screaming, yelling or talking loudly) this can cause the folds to become stiff and swollen.  
• Speaking or singing habitually at suboptimal pitch can cause a muscular imbalance. 
• Chronic coughing and throat clearing also stress the equipment. 
• Poor diet, inadequate hydration, and lack of exercise and sleep make the folds dry and more susceptible to irritation. 
• Habits that stress the neck, chin, and jaw muscles may have a negative effect on the voice. 
• Substances such as  tar, nicotine, alcohol, caffeine, antihistamines, decongestants  can all have a bad affect on the voice.  
• Gastric Esophogeal Reflux disease can wreak havoc with the vocal folds as well.

What you can do: 

• Drink 8-10 glasses of liquid a day. 
• Use a humidifier or breathe through a wet cloth to keep the relative humidity at 40% or more.
• Rest your voice after periods of extended use.
• Get outdoors as much as possible and exercise while you're at it.
• Learn to decouple unnecessary muscles.  This may require voice therapy, singing lessons, or speaker coaching.
• Get adequate sleep and eat a good diet.
• If you have GERD, avoid greasy spicy or gaseous food and drinks.  Stay upright after eating. You might wish to consider a raw foods diet.  Some singers claim they have completely cured GERD with this diet 
• If you have laryngitis, cease and desist with all talking until it is better.
• If you have a vocal distress that does not improve with these treatments after ten days, consult your otolaryngologist. You could have nodules or cancer or something else serious.