Simple, because your baby doesn`t know how to blow the mucus from their nose when they has a cold!!!
Meanwhile, the FDA strongly recommends that over-the-counter (OTC) cough and cold products should not be used for infants and children under 2 years of age because serious and potentially life-threatening side effects could occur. 
In short, nasal aspirator is the safest way to help your baby breathe freely.
Choosing Your Best Nasal Aspirator
• Bulb – cheap, good for thin mucous, and are not really designed to be used more than once because they are hard to clean.
• Human Suction - generates a vacuum by you sucking on the mouthpiece.
But don`t worry, almost all of them have a replaceable filter system; designed to prevent germs from reaching your mouth.
They give you control over high suction and very easy to clean.
However, there is still a possibility that you can catch the same cold as your infant.
• Electric - provide continuous, gently suction without making you to squeezing or sucking.
However, the batteries need replacing, weaker suction, and suction is not adjustable. 
2. Other Features To Consider:
• BPA & Phthalate free.
• Easy to clean or dishwasher safe.
3. What Other Users Have Said
There is a great advantage if you buy your nasal aspirator online is that you can see directly the opinions of other users.
And that is why large and trusted online retailer like Amazon.com displaying their customer reviews including the star rating. It will give you a real picture of a product you plan to buy.
The more the number of buyer reviews and the higher the star rating, the better the product in the eyes of consumers.
For your information, people who can submit a product review on Amazon.com must make the purchase first. So rest assured, you will get an honest review from them.
Now, get yours!!!
Top 10 Best Nasal Aspirators
1. NoseFrida The Snotsucker (under $14)
• Reviewed by 7.068 verified buyers - 4.6 out of 5 stars - READ REVIEWS
• Doctor invented and recommended nasal aspirator that uses parents' own suction to effectively clear babies' stuffy noses.
• NoseFrida creates a seal with the outside of the baby's nostril for seamless, comfortable snotsucking
• Disposable filters are clinically proven to prevent transfer of mucus or bacterial germs.
• BPA & Phthalate free.
• Easy to clean, most parts are top-rack dishwasher safe.
• Dimensions: 7.1 x 3 x 1 inches, 2.1 ounces
2. Bubzi (under $15)
• Reviewed by 1.564 verified buyers - 4.6 out of 5 stars - READ REVIEWS
• Removes Nasal Congestion Caused By Colds, Flu's and Allergies in 30 seconds or Less To Protect Your Baby's Health
• Hospital Grade Soft Silicone Tip is Designed to Fit Comfortably Into Your Baby's Nose; Hospital Grade Snot Sucker is BPA-Free and Contains No Harmful Plastics
• Designed For Parents That Don't Know What They Are Doing, Our Simple Nasal Aspirator Helps You Clear Child Congestion Fast Without Causing Any Extra Discomfort
• Cleans In Seconds. Just Put Under Running Water. No More Worrying About Mold Or Making Your Baby Sick Unlike Traditional Nose Bulb Aspirators. Plus No Need For Filters Like Nose Frida Or Electric Aspirators
• Dimensions: 4.5 x 3 x 1.2 inches, 2.4 ounces
3. Graco NasalClear (under $19)
• Reviewed by 1.321 verified buyers - 3.7 out of 5 stars - READ REVIEWS
• 12 different children's tunes while in use, help divert your child and comfort her while clearing her nasal passages
• Battery operation lets you control the suction you maintain the suction or release it as needed
• Soft, flexible silicone tips make it gentle and comfortable to use even on a newborn baby
• Silicone tip for different nostril shapes and different types of congestion
• Clear plastic collection cup helps you evaluate your baby's level of congestion
• 1-year warranty
• Dimensions: 9.2 x 5.6 x 1.9 inches, 8.8 ounces
4. BabyBubz Baby Booger Remover (under $10)
• Reviewed by 759 verified buyers - 4.7 out of 5 stars - READ REVIEWS
• Help your child to breathe, eat and sleep better - absolutely essential cold relief for infants
• Humidifiers and childrens cold and flu medications are the first step, but you need this ingenious device to be 100% sanitary
• Keep that messy little nose from ruining infant and toddler outerwear jackets
• Most effective, safest way to clear your infant's or toddler's nose, no more saline nasal sprays
• Hospital grade, BPA and Phthalate free. Safe because you decide how much suction to use on your infant - !00% Satisfaction Lifetime Guarantee
• Dimensions: 7 x 4 x 1 inches ; 1.6 ounces
5. Pediatrician Choice (under $8)
• Reviewed by 557 verified buyers - 4.3 out of 5 stars - READ REVIEWS
• Recommended by Pediatricians: safe and doctor-approved for the smaller noses of newborns, infants, and toddlers.
• Quickly Suctions Nasal Congestion: YOU control the suction strength in order to keep your baby comfortable.
• No Icky Meds or Moldy Bulbs.
• Easy to Take Apart and Clean: You can reuse our aspirator over and over. When you're finished suctioning, simply wash all components in warm water. No expensive filters to replace!
• Dimensions: 3 x 5 x 7 inches; 0.3 ounces
6. BoogieBulb (under $15)
• Reviewed by 554 verified buyers - 4.2 out of 5 stars - READ REVIEWS
• HOSPITAL GRADE NOSE SUCTION.
• BPA, Phthalate, Latex Free
• Simply twist back on after cleaning to reuse. Soft Rubber and Narrow Tip syringe make it easier to suction the snot out of your baby girl or baby boy nose.
• EASY TO CLEAN and dry to completely eliminate mold build up.
• Dimensions: 3 x 7 x 5.5 inches; 0.3 ounces
7. NeilMed Naspira (under $10)
• Reviewed by 437 verified buyers - 4.7 out of 5 stars - READ REVIEWS
• Transparent design,Sterilizable,Safe for babies & toddlers
• Contains in-line disposable filters to reduce contamination risk
• Components pull apart for easy cleaning
• 2-in-1 design allows for use as both a bulb and an aspirator
• Lifetime warranty,Made of high-grade silicone,Dishwasher safe (excluding disposable filters)
• Transparent design,Sterilizable
• Made of high-grade silicone,Dishwasher safe (excluding disposable filters)
• Dimensions: 2.2 x 4.2 x 7.2 inches ; 4 ounces
8. Bloom Baby Care (under $16)
• Reviewed by 300 verified buyers - 4.5 out of 5 stars - READ REVIEWS
• Your baby will be free of congestion in less than one minute!
• Soft silicone tip, your little one stays comfortable and relaxed while the effective suction seal provides nasal relief in seconds.
• Comes with durable parts that clean in seconds in hot, soapy water or the top rack of a dishwasher. Plus it includes a compact carrying case - great for diaper bags or home storage.
• Medical-grade BPA FREE SILICONE and FILTER FREE.
• Dimensions: 6.2 x 4.8 x 1.4 inches; 1.9 ounces
9. OccoBaby (under $35)
• Reviewed by 282 verified buyers - 4.1 out of 5 stars - READ REVIEWS
• EXCLUSIVE POWER SUCTION TIP, BATTERIES and a BONUS SNOT SUCKER.
• FITS ANY NOSE - 3 SIZES OF SOFT REUSABLE SILICONE TIPS provide the perfect suction for every size nose.
• Medically tested, FDA approved and constructed upon the highest quality and safety standards. Safe for newborns and toddlers while still powerful enough to suck all the mucus, boogers and snot out in seconds!
• WATERPROOF AND SUPER EASY TO CLEAN - simply open the mucus cup and rinse with hot soapy water.
• Dimensions: 1.8 x 7.5 x 1.8 inches; 10.1 ounces
10. Mom`s Choice (under $30)
• Reviewed by 263 verified buyers - 4.0 out of 5 stars - READ REVIEWS
• Powerful but gentle suction to suck out mucus and boogies.
• Simply hold nasal aspirator with one hand and press the button to start suction. To stop, simply release button.
•WATERPROOF & EASY TO CLEAN: Simply pop off mucus collection cup and rinse out with hot water after each.
• INCLUDES TWO SIZES OF SILICONE TIPS & EXTRA SET OF "O" RINGS.
• Dimensions: 1.8 x 1.8 x 7.5 inches; 9 ounces