Dear Doctor: Like millions of other women, I've always slathered myself with moisturizers and creams without paying any attention to the ingredients. But recently I read that the parabens found in these products have also been found in breast tissue. Should we rethink our use of these creams?

Dear Reader: That's a smart question to ask. Before we explore the data, let's take a look at what parabens are and what they do. These are chemicals used as preservatives in commercial moisturizers, shampoos, shaving gels, sunscreens and makeup. They were first used nearly 100 years ago to preserve drug products and are still used to preserve drugs applied to the skin, injected into veins and taken by mouth. Lastly, parabens are used as a preservative in multiple food products.

Parabens are good preservatives because they have antibacterial properties as well as activity against yeast and molds. They also don't allow water to enter or break down the product they are preserving. Parabens are relatively inexpensive to make and are considered generally safe for food consumption by the Food and Drug Administration and European Union.

The widespread use of parabens, however, leads to their deposit in unintended places. Parabens are found at various concentrations in indoor dust and air. The potential health effects are more concerning in children than in adults, because their ingestion rate of parabens from dust is five to 10 times higher. In addition, parabens can end up in wastewater, ultimately sending them into the water supply, agricultural soil and fish, which leads to higher paraben exposure through consumption of fish and food products. One good aspect of parabens is that they are quickly eliminated from the body, so it is less likely they will build up over time.

As for the health effects, the primary concern is about parabens' effect on sex hormones. Parabens can bind to estrogen receptors in the body, meaning they have an estrogenlike effect that could potentially raise breast cancer risk and impact fertility. They also can bind to testosterone receptors, potentially affecting male fertility as well. In rats, very high doses of parabens decrease levels of estrogen and testosterone and cause menstrual irregularities in females and alterations in sperm counts in male.

A study of 501 couples actively attempting pregnancy in Michigan and Texas supports concern over parabens. Researchers measured urinary levels of parabens in both men and women and found that women with the highest amounts of parabens in their urine had a 34 percent reduction in pregnancy compared to women with the lowest amounts in the urine.

Parabens have been found in both breast tumors and in the breast tissue adjacent to tumors. This doesn't mean that parabens cause breast cancer, but it also doesn't mean we should simply call them innocuous.

Also, in humans, higher levels of parabens in the urine have been associated with lower levels of thyroid hormones, although this potential link is clouded by the fact that women use more parabens than men and also have more thyroid problems. Lastly, parabens applied to the skin, in combination with UVB light, can increase the risk of skin damage and possibly skin cancer.

In short, parabens at current human exposure may not cause harm. But with greater use and with greater accumulation of parabens in our food and water supply, we should all ask questions about their future health effects.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I just read about a study that says exercise cancels out alcohol's higher risk of death from cancer. Is it possible that I can walk off the cancer risk of the cocktail I have each night after dinner? (For the record, my husband is sure that you're going to say no.)

Dear Reader: While we commend your creative thinking, your husband has guessed right. In our opinion, you can't depend on added exercise to cancel out the increased risk of cancer that can be caused by alcohol consumption. It's not that we think the study itself is wrong. It's the way the results have been interpreted in some news stories -- as cause and effect -- that is, at best, misleading.

Let's start from the beginning.

Researchers in England looked at a decade of medical data collected from 36,370 women and men, all 40 or older. They sorted the study subjects by how much alcohol they consumed and by how much they exercised.

Not surprisingly, they found a statistical link between "hazardous drinking" and an increased risk of death from all causes, including cancer. In this study, hazardous drinking was defined as 8 to 20 servings of alcohol per week for women, and 21 to 49 servings of alcohol for men.

Then the researchers included exercise as a variable in their calculations. They found that among people who spent at least 150 minutes per week doing moderate aerobic activity, like a brisk walk, the mortality rate due to cancer dropped. This proved to be true even among the heavier drinkers, as long as they exercised.

On its face this seems to suggest, as many news reports went on to state, that exercise can cancel out the elevated risk of cancer due to drinking. But -- and this is crucial -- this is what's known as an observational study. That means the study is based solely on data collected from the same subjects over a period of time.

While studies like these are useful for pointing out the existence of certain patterns based on the information at hand, they can't be used to prove cause and effect. The level of exercise among the drinkers is just one among countless variables that can play a role in whether someone goes on to get cancer. These variables include genetics, family history, diet, environmental causes, and levels of stress and anxiety, to name just a few. Even how forthcoming and reliable the study's subjects were in self-reporting their drinking and exercise habits would have an impact on the outcome.

That said, what this study does do is add to the significant body of existing evidence that exercise plays a role in good health. Exercising may not automatically equal risk-free drinking, but people who exercise regularly do get some pretty great benefits. It can help maintain weight, aid in weight loss, bolster cardiovascular health and play a role in maintaining healthful blood lipid levels. It can also help with sleep and boost mood.

Get your husband on board and maybe instead of a nightly cocktail, the two of you can head outside after dinner for a companionable (and brisk) walk.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My husband has seemed really down since the birth of our son six months ago. We're both being run ragged, and very proud of our son, but my husband seems less happy than I had hoped he would be. Could he be suffering from postpartum depression? If so, how? I'm the one with the hormonal onslaught!

Dear Reader: "Running ragged" is a good description of parents in the first year of a child's life. Many have described it as going into a tunnel. Metaphorically, it can get mighty dark in there. Parents and their new child grope around to find some sense of normalcy, when every day brings a new change or a new obstacle. Adding to these challenges for women is the drop in the hormones estrogen, progesterone and oxytocin after pregnancy, which can trigger mood fluctuations and postpartum depression. Men don't have that same hormonal drop, but that doesn't mean they don't experience changes.

Studies in mammalian fathers, including humans, who take care of newborns have shown drops in their testosterone levels after birth and a rise in their levels of prolactin, a hormone typically linked to a female's ability to produce milk. Evolutionarily, it makes sense that men who are helping to take care of children should have a drop in testosterone. Testosterone is needed for procreation, which should be the last thing on a dad's mind when he's taking care of a child. In fact, studies in multiple societies have found that the more hours a father invests in childcare, the lower his testosterone level will be.

A recent study in the journal Hormones and Behavior attempted to evaluate levels of testosterone and postpartum male depression in 149 low-income males (30 percent had household incomes below the poverty line). Fathers and mothers were assessed for postpartum depression, parenting stress, relationship satisfaction and intimate partner aggression. These assessments were performed one to three months after birth, six to nine months after birth and 12 to 16 months after birth. Also, at nine months after birth, the fathers underwent salivary testosterone testing.

Lower testosterone in fathers at nine months after birth correlated with increased depressive symptoms at that time, but not when depression was tested again at 15 months. Men with depressive symptoms at nine months also reported increasing parenting stress six months later. Interestingly, though, lower testosterone in the father at nine months was associated with less postpartum depressive symptoms in the female partner at nine months and 15 months.

The men with higher testosterone levels had decreased depressive symptoms at one to three months after birth, but this did not hold true at the six-to-nine month and 12-to-16 month intervals. However, the female partners of the men with higher testosterone levels reported more depressive symptoms and more feelings of aggression from their partner at the six-to-nine and 12-to-16 month intervals. Also, men with higher testosterone levels had increased parenting stress at 15 months.

The findings are complex, but they show that hormone levels do indeed fluctuate in men, affecting their psyche, their outlook and their relationships. Specifically, higher and lower levels of testosterone are linked to psychological changes in both parents.

As you know, being a parent isn't easy. Aside from the hormonal changes, parents of both genders can face financial pressures, sleep deprivation and the realization that life has changed dramatically. Each person processes and adjusts differently. My advice: Keep communicating. Your son will benefit from it.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)