Holyrood’s social security committee is carrying out the inquiry in a bid to determine what can be done to improve uptake.
Fewer than a third (31 per cent) of families without children who were eligible for working tax credit claimed the benefit in 2016-17, figures from HM Revenue and Customs and the UK Department for Work and Pensions estimated.
Only 60 per cent of those eligible for pension credit signed up for it.
Difficulties in estimating the number of people not taking up benefits means the full extent of the problem is unknown.
MSPs will now consider if information campaigns could boost take-up, or if technology could be used to automate the process and make it easier.
Committee convener Bob Doris said: “There can be any number of reasons for low benefit uptake rates but it is absolutely essential that we learn the scale of this challenge and take every possible action to improve uptake.
“There is no doubt the stigma of claiming benefits hinders uptake, while too often people are simply not aware of the benefits they are entitled to.
“Administration processes are also often too complex and our inquiry is determined to identify any barriers to benefit uptake and how we can remove these.
“The committee will consider the Scottish Government strategy on benefit uptake, which will be published in October, but what is clear is that everything possible must be done to ensure those in need receive the full benefits they are entitled to.”
Other issues the committee is keen to explore include if different approaches are required for different benefits and the impact of various eligibility criteria upon take-up rates.
The committee held an evidence session in March on pension credit and the changes to the rules for eligibility for mixed-age couples.
It came amid concerns the announcement had been “snuck out” by means of a written statement on the same day as one of the meaningful votes on Brexit. There were also concerns about a lack of information or breakdown provided on how many people it was anticipated the change might impact in its first year.
The committee subsequently agreed to write to the UK Government calling for a delay of six months in introducing this change to improve the level of uptake before the deadline.