M2T - In your case it seems absolutely clear that your ds's asthma is inherited as it is so prevalent in your family. I really don't believe in this link - the study was so small, it was on mice and it didn't even provoke asthma attacks in them! It also came out of a pressure group, which always rings alarm bells with me.
Disposable nappies also have a breathable cover. I think testing terries without wraps or plastic pants is completely misleading. Also the study has not be replicated, which speaks volumes to me about it not being very reliable.
I thought the following report from ABC news in the US was useful at putting both sides. I would do it as a link, but I have never yet done a succesful link.
Hot Under the Diaper?
German Researchers Say Diapers Raise Scrotum Temperature, Possibly Leading to Future Sperm Decline
Will your baby son be able to have babies someday? Researchers worry disposable diapers could lead to male infertility. (ArtToday)
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By Melissa Schorr
B O S T O N, Sept. 25 ? Could diapers be causing a rash ? of male infertility?
    German researchers say the wide use of disposable diapers may be one explanation for the worldwide decline in male sperm counts documented in recent decades. But several experts decry the soiling of diaper?s clean image.
    The study, which was published in the Archives of Disease in Childhood, found that male babies who wear plastic rather than cotton diapers had a significant rise in scrotum temperature, which the researchers theorize may cause infertility problems later in life. The scrotum is the external sac of skin that encloses the testes, where the body makes sperm.
Plastic Vs. Cotton
The researchers placed 48 babies in plastic Pampers and cotton diapers and compared their scrotal temperatures for the next 24 hours. They found a 1 degree Celcius rise in the babies who wore plastic diapers, or ?nappies.?
    ?The physiological testicular cooling mechanism is blunted and often completed abolished during plastic nappy use,? somberly write the authors, led by Dr. C.J. Partsch, a pediatric endocrinologist at the University of Kiel in Germany. ?The impact of a temperature increase on the developing testis is unknown.?
    Although a rise in temperature has been shown to harm sperm development in adults, it remains unclear what the impact of the heat could have on babies.
    Urology experts agree a 1 degree to 3 degree Celsius rise in testis temperature has been shown to harm sperm development and motility in adults, says Grace Centola, president of the Society for Male Reproduction and Urology in Bryn Mawr, Pa.
Testes Need Cooler Environment
That?s because testicles need to be around 3 degrees cooler than the body?s normal temperature for ideal sperm production; thus, their anatomical banishment outside of the body. Men striving towards fatherhood are advised to avoid tight briefs and hot tubs to better their chances.
    But an infant?s developing testicles won?t begin producing sperm until puberty is reached at least a decade later and some experts doubt the slight rise in temperature could have a later affect on infertility.
    During the time of infancy, the cells that will later become sperm cells are still just normal cells that probably are unaffected by the change in heat, says Dr. Bruce Gilbert, associate clinical professor of urology at the State University of New York at Stonybrook. ?Does [increased temperature] really make a difference at that time?? Gilbert says. ?Anything early on is speculation.?
    One piece of support for the German researchers? position is that babies whose testes don?t descend outside the body but remain stuck inside for a year often have a lowered sperm count later in life.
    But this just may be because their testes were damaged originally, not because the body?s higher temperature caused the damage, says Dr. Larry Lipshultz, professor of urology at Baylor College of Medicine in Houston, Texas.
    Without following diaper users into the future, or looking back at infertile men?s diaper use as a babe, the study raises more questions than it answers.
    ?It?s food for thought,? the male reproductive society?s Centola says. ?It may warrant further, long-term studies. I?d want to see the data 40 years down the road.?
Sperm Decline Debatable
Whether or not diaper use is one of the factors contributing to an overall decline in sperm counts of the current generation of men compared their grandfathers is highly debatable.
    For one thing, experts still squabble over whether or not this decline is really taking place. A 1992 analysis of 61 earlier studies found a worldwide sperm count decline of 1.5 percent annually from 1938 to 1990 ? but later studies contradicted those results.
    ?It?s controversial,? Stonybrook?s Gilbert says. ?There is no great opinion on whether there really has been a decline.?
    Those who believe there has been a decline in sperm counts attribute it to everything from environmental toxins to higher rates of sexually transmitted diseases to global warming.
    Disposable diapers, which made their way onto store shelves around 35 years ago, may be part of the mix, the researchers suspected.
Defending the Diaper
But the manufacturers of Pampers and Luvs, feeling the heat, spring to diaper defense.
    ?The trend in decreased fertility has been noted for the past 60 years,? says Khristin Heaney, a spokeswoman for the Personal Absorbent Product Council, a Washington D.C.-based trade group. ?But we?ve only been using diapers for 35 years, which would lead me to believe there?s more at issue.?
    Heaney says the diaper?s record is spotless ? it?s the study that is sullied. She says a prominent expert has said the probes used by the researchers couldn?t be accurately applied to an infant?s scrotum.
    ?Thirty-five years of clinical and safety studies have never led anyone to believe there was an issue,? Heaney adds. ?In industry research, skin temperature tests which monitored the temperature in the overall diaper area found no increase indicated. Clearly, it?s a non-issue.?