In the case of cats, data does suggest that over exposing children between the ages of 12-14 to cats does not lead to sensitization to cat allergens but does lead to increased levels of IgG antibody response. In contrast, data regarding increased mite allergen exposure does induce a sensitization to the allergen while levels of IgG4 also increase. As the graph below indicates, sensitization to cat allergen decreased as the concentration of cat allergen increased.

(Platts-Mills, et al. 2001)

Recent studies have also indicated that houses with pet reduce the occurrence of asthma in children. The data from the cat allergen experiment would seem to support these recent studies.

What is not known:

At this point in time, only data for cat allergen desensitization can be found. Data has not yet been collected in regards to any of the other prolific allergens found indoors or outdoors. To make things more uncertain, some scientist state the opposite is true even in the case of cats (Almqvist C. 2005). To say the least, among the scientific community this is still a controversial subject.

How can this question be answered?

The same experiment involving cat dander can be used to test whether dog dander produces similar results. This would help determine whether or not most allergens reduces sensitization at higher concentrations. After examining the data on the mite allergen, it may also be possible that the concentration of mite allergen was not large enough to illicit the same response as the cat allergen. A follow up study could also be conducted to reanalyze the dust mite data.

Can asthma or asthma medications hurt the developing fetus during a pregnancy?

What is currently known:

Table. 1— Historical cohort studies examining the effect of maternal asthma on pregnancy outcomes

Author yr [ref]	Population study yrs	Asthma definition	Sample size	ICS use	Poor outcomes associated with asthma	Poor outcomes not associated with asthma
Gordon et al., 1970 9	USA	Actively treated asthma	30861 (all) 277 (asthma)	Prior to ICS	Perinatal death (severe asthma)	Low birth weight
Bahna and Bjerkedal, 1972 10	Norway 1967–1968	Mother's health documented by midwife or physician in birth registry	112530 (control) 381 (asthma)	Prior to ICS	Pre-term delivery, low birth weight, hyperemesis, haemorrhage, toxemia, induced/complicated labour, neonatal mortality
Lao and Huengsburg, 1990 11	Hong Kong 1984–1987	History of asthma	87 (control) 87 (asthma)	11% used beclomethasone	Low birth weight (mothers not receiving treatment for asthma), C-section (mothers using bronchodilators)
Perlow *et al*., 1992 12	USA 1985–1990	Asthma diagnosis reported in perinatal database	130 (control) 81 (asthma)	Unclear	C-section for foetal distress, pre-term labour and delivery, pre-term premature rupture of membranes, gestational diabetes (steroid-dependent asthma), low birth weight (steroid-dependent asthma)	Pre-eclampsia, chronic hypertension, congenital malformations, IUGR
Lehrer *et al*., 1993 13	USA 1987–1991	Asthma history or asthma requiring treatment	22680 (control) 1435 (asthma history), 136 (asthma with treatment)	136 used ICS	Pregnancy-induced hypertension
Demissie *et al*., 1998 14	USA 1989–1992	Asthma diagnosis recorded in database	9156 (control) 2289 (asthma)	Unknown	Pregnancy-induced hypertension, pre-eclampsia, low birth weight, pre-term delivery, congenital malformations	Post-partum haemorrhage
Alexander *et al*., 1998 1	Canada 1991–1993	Completed on prenatal records or maternal admission forms	13709 (control) 817 (asthma)	Unclear	Antepartum and post-partum haemorrhage	C-section, gestational diabetes, pre-term delivery, pregnancy-induced hypertension
Kallen *et al*., 2000 15	Sweden 1984–1995	Recorded by midwife	36985 (all pregnant females) 15512 (asthma)	Unknown	Pre-term delivery, low birth weight, post-term birth, infant death	Congenital malformations
Wen *et al*., 2001 16	Canada 1989–1996	Diagnosis recorded in database	34688 (control) 8672 (asthma)	Unknown	Pre-term labour, pre-eclampsia, pregnancy-induced hypertension, antepartum and post-partum haemorrhage, premature rupture of membranes, C-section	Foetal death
Liu *et al*., 2001 17	Canada 1991–1996	Diagnosis recorded in database	8772 (control) 2193 (asthma)	Unknown	Small for gestational age, pregnancy-induced hypertension, chorioamnionitis, pre-eclampsia, pre-term delivery	Congenital malformations
Olesen *et al*., 2001 18	Denmark 1991–1996	Primiparae females with diagnosis of asthma and purchase of prescription drugs for asthma	8717 (control) 303 (asthma)	22.5% used ICS	Small for gestational age (theophylline users), reduced birth weight and length (mothers who reduced intensity of drug treatment during pregnancy)	Congenital malformations
Norjavaara and de Verdier, 2003 19	Sweden 1995–1998	Self-report	293948 (all) 2968 (asthma)	All used budesonide	C-section	Still birth, congenital malformations, reduced birth weight, reduced gestational length

ICS: inhaled corticosteroid; C-section: caesarean section; IUGR: intrauterine growth restriction http://erj.ersjournals.com/cgi/content/full/25/4/731

The many studies comparing mothers with asthma and mothers without asthma shows that asthmatic mothers are more at risk of giving birth before the due date or giving birth to low weight neonates.

What is not known:

The mechanisms leading the complications during the pregnancy and birth. Why asthmatic female are more likely to give birth to low weight neonates.

How can this question be answered?

The difficulty of answering this question involves developing an experimental method that would allow researchers the ability to analyze the differences between asthmatic females during pregnancy so that both the female and fetus is not harmed. Experiments monitoring the oxygen levels in the blood of females may help answers some questions. Murine experiments involving asthmatic females may be the best way to explore the effects of maternal asthma on embryonic development. The effects of asthma medications on embryonic development could also be examined using mice too. Giving female mice asthma medication during a pregnancy then examining the fetuses for any abnormal development could elucidate the mechanisms behind the changes in a pregnancy as a result of asthma.